Method for increasing the fouling resistance of inorganic membranes by grafting with organic moieties

ABSTRACT

Provided herein are filtration membranes for water treatment, and methods for preventing fouling of such membranes. The method described herein comprises grafting the membrane surface with an organic moiety, by reacting the surface with an organometallic reagent, a phosphonate, a phosphinate, or an organosilane.

FIELD OF THE INVENTION

The present application relates to the field of filtration membranes,more particularly ceramic membranes for water purification, and tomethods for preventing or diminishing fouling of such membranes.

BACKGROUND OF THE INVENTION

Availability of clean water is a growing world-wide challenge.Consequently, development of efficient water purification, desalinationand recycling technologies is an important topic on the world-wideresearch agenda.

Membrane filtration is considered a very powerful purificationtechnology to tackle this problem. The majority of the membranes usedfor water filtration have long been polymeric membranes. However, morerecently also ceramic membranes are finding their way into this field.The main benefits of ceramic membranes are their high chemical andthermal stability enabling chemical and/or thermal regeneration andsterilization by aggressive chemicals and/or hot steam. Moreover, theirhigh mechanical stability enables high pressure back-flushing. As aconsequence, despite their higher cost, ceramic membranes are becomingan economically feasible alternative for polymeric membranes in watertreatment.

A critical issue in the development of effective membrane processes(both for polymeric and ceramic membranes) is the decline in systemperformance due to membrane fouling. This limits the economic efficiencyof the operation and slows down large scale industrial applications ofmembranes especially in case of fouling caused by the adsorption ofdissolved matter onto the membrane surface and/or into the membranepores. This type of fouling is considered irreversible fouling and cangenerally only be removed by chemical cleaning.

Membrane fouling can be decreased by optimization of feed pre-treatment(e.g. via ultrafiltration, microfiltration, flocculation, ozonationand/or UV oxidation), and regular physical and chemical cleaning.Additional measures involve a careful selection of membrane, moduledesign, and operating parameters.

A more sustainable approach is the prevention of the undesiredadsorption processes by membrane-surface modification. Although poorlyunderstood, it is generally accepted that fouling of polymeric membranesin water treatment decreases with an increase in hydrophilicity of themembrane material. Consequently, research has been performed to increasepolymer membrane hydrophilicity by grafting, plasma or other surfacetreatment.

Ceramic membranes, and particularly silicon and/or metal oxide andhydroxide membranes, generally are intrinsically hydrophilic andconsistently show relative low fouling in water treatment. Nevertheless,also these membranes become less effective over time due to fouling.

Grafting of ceramic materials with phosphonic acids is known to resultin stable modified metal oxide surfaces (Mutin et al.; J. Mater. Chem.2005, 15, 3761). International patent application WO 2010/106167describes another stable grafting of organic functional moieties ontothe surface of ceramic membranes in order to increase the membranehydrophobicity or change its affinity.

SUMMARY OF THE INVENTION

The present inventors surprisingly found that by grafting silicon ormetal oxide and/or hydroxide membranes with certain organic moieties,the sensitivity of the membranes to fouling decreases significantly,while maintaining sufficient hydrophilicity.

Thus, provided herein is a method for reducing the sensitivity of amembrane comprising an oxide and/or hydroxide of silicon or a metal tofouling and/or protecting a membrane against fouling comprising graftingthe surface of said oxide and/or hydroxide with an organic moiety R¹ orR¹⁰ by contacting said surface with an organometallic reagent, aphosphonate, a phosphinate, or an organosilane.

The method is further characterized in that R¹ is selected from thegroup consisting of C₁₋₁₂alkyl, C₆₋₁₀aryl, C₇₋₁₆alkylaryl,C₇₋₁₆arylalkyl, —R⁷[OR⁸]_(n)R⁹, C₃₋₈cycloalkyl, C₃₋₈cycloalkenyl,C₄₋₁₀cycloalkylalkyl, C₄₋₁₀cycloalkenylalkyl, C₂₋₁₂alkenyl, 3- to8-membered heterocyclyl, 5- to 10-membered heteroaryl,heterocyclylC₁₋₆alkyl, heteroarylC₁₋₄alkyl and C₂₋₁₂alkynyl; wherein R⁷and R⁸ are independently from each other C₁₋₄alkylene; n is an integerfrom 1 to 4; and R⁹ is C₁₋₄ alkyl; and

R¹⁰ is selected from the group consisting of C₁₋₈ alkylene,C₆₋₁₀arylene, C₇₋₁₆alkylarylene, C₇₋₁₆arylalkylene, —R¹¹[OR¹²]_(m)R¹³—,C₃₋₈cycloalkylene, C₃₋₈cycloalkenylene, C₄₋₁₀cycloalkylalkylene,C₄₋₁₀cycloalkenylalkylene, C₂₋₁₂alkenylene, 3- to 8-memberedheterocyclylene, 5- to 10-membered heteroarylene,heterocyclylC₁₋₆alkylene, heteroarylC₁₋₄alkylene and C₂₋₁₂alkynylene;wherein R¹¹, R¹², and R¹³ are independently from each otherC₁₋₄alkylene, and m is an integer from 1 to 4;

wherein R¹ and R¹⁰ are optionally substituted with one or more groupsindependently selected from hydroxyl, —OR⁴, amino, halo, sulfhydryl,—SR⁵, —COOH, and —COOR⁶; wherein R⁴, R⁵, R⁶ are independently selectedfrom C₁₋₆alkyl, halo and C₆₋₁₀aryl.

In particular embodiments, the membrane comprises an oxide and/orhydroxide of an element M¹, and said surface of said inorganic matrix isgrafted with an organic functional group R¹, via a direct M¹-R¹ bond; atleast one M¹-O—P—R¹ bond; a M¹-O—Si—R¹ bond; a M¹-O—P—R¹⁰—P—O-M¹ bond;or a M¹-O—Si—R¹⁰—Si—O-M¹ bond; wherein M¹ is a metal or silicon; and R¹and R¹⁰ have the same meaning as defined above.

In certain embodiments, the organometallic reagent is a compound of theformula R¹-M², or of formula R¹-M²-X, or of formula R¹-M²-R^(1′);wherein M² is Li or Mg, and X is halo; R¹ has the same meaning asdefined above; and R^(1′) is, the same or different from R¹, selectedfrom the group consisting of C₁₋₁₂alkyl, C₆₋₁₀aryl, C₇₋₁₆alkylaryl,C₇₋₁₆arylalkyl, —R⁷[OR⁸]_(n)R⁹, C₃₋₈cycloalkyl, C₃₋₈cycloalkenyl,C₄₋₁₀cycloalkylalkyl, C₄₋₁₀cycloalkenylalkyl, C₂₋₁₂alkenyl, 3- to8-membered heterocyclyl, 5- to 10-membered heteroaryl,heterocyclylC₁₋₆alkyl, heteroarylC₁₋₄alkyl and C₂₋₁₂alkynyl; optionallysubstituted with one or more groups independently selected fromhydroxyl, —OR⁴, amino, halo, sulfhydryl, —SR⁵, —COOH, and —COOR⁶;wherein R⁴, R⁵, R⁶ are independently selected from C₁₋₆alkyl, halo andC₆₋₁₀aryl; R⁷ and R⁸ are independently from each other C₁₋₄alkylene; nis an integer from 1 to 4; and R⁹ is C₁₋₄ alkyl.

In particular embodiments, the phosphonate or phosphinate is a compoundchosen from

-   -   formula (I)

-   -   or a salt or ester thereof, wherein R¹ has the same meaning as        defined above;    -   or    -   formula (III)

-   -   or a salt or ester thereof, wherein    -   R¹ has the same meaning as defined above; and    -   R^(1′) is, the same or different from R¹, selected from the        group consisting of C₁₋₁₂alkyl, C₆₋₁₀aryl, C₇₋₁₆alkylaryl,        C₇₋₁₆arylalkyl, —R⁷[OR⁸]_(n)R⁹, C₃₋₈cycloalkyl,        C₃₋₈cycloalkenyl, C₄₋₁₀cycloalkylalkyl, C₄₋₁₀cycloalkenylalkyl,        C₂₋₁₂alkenyl, 3- to 8-membered heterocyclyl, 5- to 10-membered        heteroaryl, heterocyclylC₁₋₆alkyl, heteroarylC₁₋₄alkyl and        C₂₋₁₂alkynyl; optionally substituted with one or more groups        independently selected from hydroxyl, —OR⁴, amino, halo,        sulfhydryl, —SR⁵, —COOH, and —COOR⁶; wherein R⁴, R⁵, R⁶ are        independently selected from C₁₋₆alkyl, halo and C₆₋₁₀aryl; R⁷        and R⁸ are independently from each other C₁₋₄alkylene; n is an        integer from 1 to 4; and R⁹ is C₁₋₄ alkyl;    -   or    -   formula (IV)

-   -   or a salt or ester thereof, wherein R¹⁰ has the same meaning as        defined above.

In certain embodiments, R¹ is C₁₋₆alkyl, phenyl, or —R⁷[OR⁸]_(n)R⁹;wherein R⁷ and R⁸ are independently from each other C₁₋₄alkylene; n isan integer from 1 to 4; and R⁹ is C₁₋₄ alkyl.

In particular embodiments, the membrane is a water treatment membrane.In certain embodiments, the method is for protecting the membrane fromfouling when used for water treatment.

In certain embodiments, R¹ is C₁₋₆alkyl or phenyl; and R¹⁰ isC₁₋₆alkylene or phenylene.

The membranes described herein are particularly suitable and stable foruse in filtration in that the grafting with one or more organic moietiesprevents or significantly reduces fouling of the membranes, compared tothe non-grafted filtration membranes. The hydrophilicity of the graftedmembranes is nevertheless still sufficient to allow an effective use ofthe membranes for water filtration. Moreover, the grafted membranes aretypically easier to clean, compared to the non-grafted membranes. Thus,the membranes are particularly suitable for use in water filtration.

Accordingly, the application further provides the use of afunctionalized inorganic matrix comprising an oxide and/or hydroxide ofan element M¹ for water treatment or water purification, characterizedin that the surface of said inorganic matrix is grafted with an organicfunctional group R¹ or R¹⁰, wherein,

-   -   M¹ is a metal or silicon;    -   R¹ is selected from the group consisting of C₁₋₁₂alkyl,        C₆₋₁₀aryl, C₇₋₁₆alkylaryl, C₇₋₁₆arylalkyl, —R⁷[OR⁸]_(n)R⁹,        C₃₋₈cycloalkyl, C₃₋₈cycloalkenyl, C₄₋₁₀cycloalkylalkyl,        C₄₋₁₀cycloalkenylalkyl, C₂₋₁₂alkenyl, 3- to 8-membered        heterocyclyl, 5- to 10-membered heteroaryl,        heterocyclylC₁₋₆alkyl, heteroarylC₁₋₄alkyl and C₂₋₁₂alkynyl;        wherein R⁷ and R⁸ are independently from each other        C₁₋₄alkylene; n is an integer from 1 to 4; and    -   R⁹ is C₁₋₄ alkyl;    -   and    -   R¹⁰ is selected from the group consisting of C₁₋₈ alkylene,        C₆₋₁₀arylene, C₇₋₁₆alkylarylene, C₇₋₁₆arylalkylene,        —R¹¹[OR¹²]_(m)R¹³—, C₃₋₈cycloalkylene, C₃₋₈cycloalkenylene,        C₄₋₁₀cycloalkylalkylene, C₄₋₁₀cycloalkenylalkylene,        C₂₋₁₂alkenylene, 3- to 8-membered heterocyclylene, 5- to        10-membered heteroarylene, heterocyclylC₁₋₆alkylene,        heteroarylC₁₋₄alkylene and C₂₋₁₂alkynylene; wherein R¹¹, R¹²,        and R¹³ are independently from each other C₁₋₄alkylene;    -   wherein R¹ and R¹⁰ are optionally substituted with one or more        groups independently selected from hydroxyl, —OR⁴, amino, halo,        sulfhydryl, —SR⁵, —COOH, and —COOR⁶; wherein R⁴, R⁵, R⁶ are        independently selected from C₁₋₆alkyl, halo and C₆₋₁₀aryl, and m        is an integer from 1 to 4.

In certain embodiments of the present use, R¹ or R¹⁰ is grafted on saidsurface via a direct M¹-R¹ bond; at least one M¹-O—P—R¹ bond; aM¹-O—Si—R¹ bond; a M¹-O—P—R¹⁰—P—O-M¹ bond; or a M¹-O—Si—R¹⁰—Si—O-M¹bond.

In particular embodiments of the use, M¹ is selected from the groupconsisting of titanium, zirconium, aluminium, silicon, strontium,yttrium, lanthanum, hafnium, thorium, iron, manganese, or combinationsthereof.

In certain embodiments of the use, the oxide and/or hydroxide of M¹ istitanium oxide or zirconium oxide.

In particular embodiments of the use, R¹ is C₁₋₆alkyl, phenyl, or—R⁷[OR⁸]_(n)R⁹; optionally substituted with one or more groupsindependently selected from hydroxyl, —OR⁴, amino, halo, sulfhydryl,—SR⁵, —COOH, and —COOR⁶; wherein R⁴, R⁵, R⁶ are independently selectedfrom C₁₋₆alkyl, halo and C₆₋₁₀aryl; R⁷ and R⁸ are independently fromeach other C₁₋₄alkylene; and n is an integer from 1 to 4.

In particular embodiments of the use, the functionalized inorganicmatrix is a membrane comprising a support made of inorganic materialcoated with at least one separating membrane layer made of the oxideand/or hydroxide of M¹ at the surface.

In certain embodiments of the use, the oxide and/or hydroxide of M¹ isprovided as particles in a mixed matrix membrane.

In certain embodiments, the membranes are porous with an average poresize of 0.5 nm to 200 nm.

The above and other characteristics, features and advantages of theconcepts described herein will become apparent from the followingdetailed description, which illustrates, by way of example, the claimedmethods and uses herein.

BRIEF DESCRIPTION OF THE DRAWINGS

The following description of the figures of specific embodiments ismerely exemplary in nature and is not intended to limit the presentteachings, their application or uses. Throughout the drawings,corresponding reference numerals indicate like or corresponding partsand features.

FIG. 1A: Graph illustrating the fouling tendency of grafted and nativetitania NF membranes using humic acid (HA) as a model foulant, in aconcentration of 10 mg/L in combination with a Ca²⁺ concentration of 1,2 and 4 mmol/L at two pH levels.

B: Graph illustrating the fouling tendency of grafted and native titaniaNF membranes using laminarin gum as a model foulant, in concentrations0.1, 0.25 and 0.5 mg/L.

C: Graph illustrating the fouling tendency of grafted and native titaniaNF membranes using meat peptone as a model foulant, in concentrations 5,15 and 25 mg/L.

D: Graph illustrating the fouling tendency of grafted and native titaniaNF membranes using wood extracts as a model foulant.

FIG. 2: Graph illustrating the reverse osmosis water (ROW) flux througha membrane before fouling, the foulant solution flux and the ROW fluxafter fouling. Horizontal hatching: foulant solution flux. Italichatching: ROW flux before fouling. Vertical hatching: ROW flux afterfouling.

DETAILED DESCRIPTION OF THE INVENTION

While potentially serving as a guide for understanding, any referencesigns in the claims shall not be construed as limiting the scopethereof.

As used herein, the singular forms “a”, “an”, and “the” include bothsingular and plural referents unless the context clearly dictatesotherwise.

The terms “comprising”, “comprises” and “comprised of” as used hereinare synonymous with “including”, “includes” or “containing”, “contains”,and are inclusive or open-ended and do not exclude additional,non-recited members, elements or method steps. The terms “comprising”,“comprises” and “comprised of” when referring to recited components,elements or method steps also include embodiments which “consist of”said recited components, elements or method steps.

Furthermore, the terms first, second, third and the like in thedescription and in the claims, are used for distinguishing betweensimilar elements and not necessarily for describing a sequential orchronological order, unless specified. It is to be understood that theterms so used are interchangeable under appropriate circumstances andthat the embodiments described herein are capable of operation in othersequences than described or illustrated herein.

The values as used herein when referring to a measurable value such as aparameter, an amount, a temporal duration, and the like, is meant toencompass variations of +/−10% or less, preferably +/−5% or less, morepreferably +/−1% or less, and still more preferably +/−0.1% or less ofand from the specified value, insofar such variations are appropriate toensure one or more of the technical effects envisaged herein. It is tobe understood that each value as used herein is itself alsospecifically, and preferably, disclosed.

The recitation of numerical ranges by endpoints includes all numbers andfractions subsumed within the respective ranges, as well as the recitedendpoints.

Reference throughout this specification to “one embodiment” or “anembodiment” means that a particular feature, structure or characteristicdescribed in connection with the embodiment is included in at least oneembodiment envisaged herein. Thus, appearances of the phrases “in oneembodiment” or “in an embodiment” in various places throughout thisspecification are not necessarily all referring to the same embodiment,but may. Furthermore, the particular features, structures orcharacteristics may be combined in any suitable manner, as would beapparent to a person skilled in the art from this disclosure, in one ormore embodiments. Furthermore, while some embodiments described hereininclude some but not other features included in other embodiments,combinations of features of different embodiments are also envisagedherein, and form different embodiments, as would be understood by thosein the art. For example, in the appended claims, any of the features ofthe claimed embodiments can be used in any combination.

All documents cited in the present specification are hereby incorporatedby reference in their entirety.

Unless otherwise defined, all terms used in disclosing the conceptsdescribed herein, including technical and scientific terms, have themeaning as commonly understood by one of ordinary skill in the art. Bymeans of further guidance, definitions for the terms used in thedescription are included to better appreciate the teaching of thepresent disclosure. The terms or definitions used herein are providedsolely to aid in the understanding of the teachings provided herein.

In a first aspect, the present application provides a method forprotecting a membrane comprising an oxide and/or hydroxide of silicon ora metal against fouling.

The term “fouling” as used herein refers to the blocking and/or pluggingof membrane pores during a filtration process, in a way that degradesthe membrane's performance, e.g. by a severe decline of the flux. Theterm fouling as used herein includes irreversible fouling due to organicfoulants such as humics, oils, and/or polyelectrolytes. The term“irreversible fouling” refers to the strong attachment of foulants,which cannot be removed by physical cleaning.

More specifically, the present application provides a method forreducing the sensitivity of a membrane comprising an oxide and/orhydroxide of silicon or a metal to fouling, in particular irreversiblefouling.

In particular embodiments, the present method allows for reducing theirreversible fouling of an inorganic membrane by at least 30%, comparedto the membrane prior to grafting with R¹ as described herein,preferably a least 50%. The amount of irreversible fouling can bemeasured by calculating the decline of the water flux under normalfiltration conditions, after fouling (without chemical cleaning) (seee.g. FIG. 2).

The present method for protecting a membrane against fouling comprisesgrafting the surface of the oxide and/or hydroxide with an organicmoiety. The expression “surface” as used herein is understood tocomprise the (macroscopic) outer surface as well as the inner poresurfaces of a matrix. The surface to which an organic functional groupis adhered may thus be an external surface and/or an internal surface ofthe matrix.

The resulting membranes are significantly less sensitive to fouling, andmay be used for the treatment or filtration of various compositions,including but not limited to aqueous compositions.

The methods envisaged herein are particularly suitable for protectingmembranes used in water treatment or purification against fouling.Indeed it has been found that grafting the surface of an oxide and/orhydroxide with an organic moiety ensures that the membranes aresignificantly less sensitive to typical foulants of water. Thus, themembranes described herein are of particular interest for the treatmentor purification of aqueous compositions. Accordingly, in a furtheraspect, the present application provides in the use of a functionalizedinorganic matrix comprising an oxide and/or hydroxide of a metal and/orsilicon for water treatment, characterized in that the surface of saidinorganic matrix is grafted with an organic functional group, moreparticularly the organic functional groups envisaged herein and definedas R¹ or R¹⁰. Optionally, the inorganic matrix may further be graftedwith an organic functional group R^(1′). In certain embodiments however,the inorganic matrix is not grafted with an organic functional groupother than R¹ and/or R¹⁰.

The method envisaged herein involves modification or functionalizationof a matrix. The terms “modification” and “functionalization” are usedinterchangeably herein and both refer to the covalent bonding of organicgroup(s), also defined herein as R¹ or R¹⁰, or in particular embodimentsR¹ and/or R^(1′) moieties, onto a surface of a matrix as defined herein.As will be detailed below, the covalent bonding of a group R¹ to amatrix, which is an oxide or hydroxide of a metal M¹, may be direct (viaa M¹-C bond) or indirect (via a M¹-O—P—C or M¹-O—Si—C bond). In thiscontext the terms “modified” or “surface-modified” or “functionalized”matrix should also be considered as synonyms and refer to a matrix asdefined herein, having organic compound(s) attached to their surface,including the surface of the pores within the matrix where applicable,via covalent binding.

The inventors have found that to obtain an optimal flux and antifoulingproperties, the functional groups R¹, R^(1′), and/or R¹⁰ are preferablynot too bulky. Indeed, the inventors have observed that optimalanti-fouling properties are obtained when R¹ is a group such as methylor phenyl. It has however been found that this anti-foulant property cansimilarly be obtained with organic moieties the organic moiety R¹ andR¹⁰ as defined herein below. In particular embodiments, R¹ and (ifpresent) R^(1′) are independently selected from the list consisting ofC₁₋₁₂alkyl, C₆₋₁₀aryl, C₇₋₁₆alkylaryl, C₇₋₁₆arylalkyl, —R⁷[OR⁸]_(n)R⁹,C₃₋₈cycloalkyl, C₃₋₈cycloalkenyl, C₄₋₁₀cycloalkylalkyl,C₄₋₁₈cycloalkenylalkyl, C₂₋₁₂alkenyl, 3- to 8-membered heterocyclyl, 5-to 10-membered heteroaryl, heterocyclylC₁₋₆alkyl, heteroarylC₁₋₄alkyland C₂₋₁₂alkynyl;

wherein R⁷ and R⁸ are independently from each other C₁₋₄alkylene; n isan integer from 1 to 4; and R⁹ is C₁₋₄ alkyl.

In certain embodiments, R¹⁰ is selected from the group consisting ofC₁₋₈alkylene, C₆₋₁₀arylene, C₇₋₁₆alkylarylene, C₇₋₁₆arylalkylene,—R¹¹[OR¹²]_(m)R¹³—, C₃₋₈cycloalkylene, C₃₋₈cycloalkenylene,C₄₋₁₀cycloalkylalkylene, C₄₋₁₀cycloalkenylalkylene, C₂₋₁₂alkenylene, 3-to 8-membered heterocyclylene, 5- to 10-membered heteroarylene,heterocyclylC₁₋₆alkylene, heteroarylC₁₋₄alkylene and C₂₋₁₂alkynylene;wherein R¹¹, R¹² and R¹³ are independently from each other C₁₋₄alkylene;

As indicated above, in certain embodiments, the inorganic matrix mayfurther be grafted with an organic functional group R^(1′). It isenvisaged that R^(1′), if present, is an organic moiety independentlyselected from the list consisting of C₁₋₁₂alkyl, C₆₋₁₀aryl,C₇₋₁₆alkylaryl, C₇₋₁₆arylalkyl, —R⁷[OR⁸]_(n)R⁹, C₃₋₈cycloalkyl,C₃₋₈cycloalkenyl, C₄₋₁₀cycloalkylalkyl, C₄₋₁₀cycloalkenylalkyl,C₂₋₁₂alkenyl, 3- to 8-membered heterocyclyl, 5- to 10-memberedheteroaryl, heterocyclylC₁₋₆alkyl, heteroarylC₁₋₄alkyl and C₂₋₁₂alkynyl;

In the embodiments envisaged herein, R¹, R^(1′) (if present), and R¹⁰are optionally substituted. The term “substituted” is used in thecontext of the methods described herein, to indicate that one or morehydrogens on the moiety indicated in the expression using “substituted”is replaced with a selection from the indicated group, provided that theindicated atom's normal valency is not exceeded, and that thesubstitution results in a chemically stable compound, i.e. a compoundthat is sufficiently robust to survive isolation to a useful degree ofpurity from a reaction mixture.

More particularly, as envisaged herein, R¹, R^(1′) (if present), and R¹⁰are optionally substituted with one or more groups independentlyselected from hydroxyl, —OR⁴, amino, halo, sulfhydryl, —SR⁵, —COOH, and—COOR⁶; wherein R⁴, R⁵, R⁶ are independently selected from C₁₋₆alkyl,halo and C₆₋₁₀aryl, and m is an integer from 1 to 4.

In particular embodiments, R¹ is C₁₋₁₂alkyl. In further embodiments, R¹is C₁₋₈alkyl, more particularly C₁₋₆alkyl. In yet further embodiments,R¹ is C₁₋₄alkyl. The term “alkyl” by itself or as part of anothersubstituent, refers to a straight or branched saturated hydrocarbongroup joined by single carbon-carbon bonds. When a subscript is usedherein following a carbon atom, the subscript refers to the number ofcarbon atoms that the named group may contain. Thus, for example,“C₁₋₄alkyl” means an alkyl of one to four carbon atoms. Examples ofC₁₋₄alkyl groups are methyl, ethyl, propyl, isopropyl, butyl, isobutyland tert-butyl.

In particular embodiments, R¹ is an ether or oligoether of formula—R⁷[OR⁸]_(n)R⁹, wherein R⁷ and R⁸ are independently from each otherC₁₋₄alkylene; n is an integer from 1 to 4; and R⁹ is C₁₋₄ alkyl. Thebond to the parent moiety is through R⁷. In further embodiments, R⁷ andR⁸ are independently from each other C₁₋₃alkylene; n is an integer from1 to 3; and R⁹ is C₁₋₃ alkyl.

As used herein, the term “C_(1-x)alkylene”, by itself or as part ofanother substituent, refers to C_(1-x)alkyl groups that are divalent,i.e., with two single bonds for attachment to two other groups. Alkylenegroups may be linear or branched and may be substituted as indicatedherein.

In a particular embodiment, R¹ is C₃₋₈cycloalkyl. As used herein, theterm “C₃₋₈cycloalkyl”, by itself or as part of another substituent,refers to a saturated cyclic alkyl group containing from about 3 toabout 8 carbon atoms. Examples of C₃₋₈cycloalkyl include cyclopropyl,cyclobutyl, cyclopentyl, or cyclohexyl, cycloheptyl and cyclooctyl. Inparticular embodiments, R¹ may be a cycloalkyl selected from the groupconsisting of cyclopropyl, cyclobutyl, cyclopentyl, and cyclohexyl.

In a particular embodiment, R¹ is C₃₋₈cycloalkenyl. As used herein, theterm “cycloalkenyl” by itself or as part of another substituent, refersto a non-aromatic mono- or multicyclic ring system comprising about 3 to8 carbon atoms, preferably about 5 to 8 carbon atoms, which contains atleast one carbon-carbon double bond. Preferred cycloalkenyl ringscontain 5 or 6 ring atoms, such as cyclopentenyl and cyclohexenyl.

In a particular embodiment, R¹ is a C₆₋₁₀aryl. As used herein, the term“C₆₋₁₀aryl”, by itself or as part of another substituent, refers to apolyunsaturated, aromatic hydrocarbyl group having a single ring (i.e.phenyl) or multiple aromatic rings fused together (e.g. naphthalene), orlinked covalently, typically containing 6 to 10 carbon atoms; wherein atleast one ring is aromatic. Aryl rings may be unsubstituted orsubstituted with from 1 to 4 substituents on the ring. Examples ofC₆₋₁₀aryl include phenyl, naphthyl, indanyl, or1,2,3,4-tetrahydro-naphthyl.

In a particular embodiment, R¹ is C₂₋₁₂alkenyl, preferably C₂₋₆alkenyl.The term “alkenyl” by itself or as part of another substituent, refersto an unsaturated hydrocarbyl group, which may be linear, or branched,comprising one or more carbon-carbon double bonds. When a subscript isused herein following a carbon atom, the subscript refers to the numberof carbon atoms that the named group may contain. Thus, for example,“C₂₋₆alkenyl” means an alkenyl of two to six carbon atoms. Non-limitingexamples of C₂₋₆alkenyl groups include ethenyl, 2-propenyl, 2-butenyl,3-butenyl, 2-pentenyl and its chain isomers, 2-hexenyl and its chainisomers, 2,4-pentadienyl and the like.

In a particular embodiment, R¹ is C₂₋₁₂alkynyl, preferably C₂₋₆alkynyl.The term “alkynyl” by itself or as part of another substituent, refersto an unsaturated hydrocarbyl group, which may be linear, or branched,comprising one or more carbon-carbon triple bonds. When a subscript isused herein following a carbon atom, the subscript refers to the numberof carbon atoms that the named group may contain. Thus, for example,“C₂₋₆alkynyl” means an alkynyl of two to six carbon atoms. Non limitingexamples of C₂₋₆alkynyl groups include ethynyl, 2-propynyl, 2-butynyl,3-butynyl, 2-pentynyl and its chain isomers, 2-hexynyl and its chainisomers and the like.

In a particular embodiment, R¹ is heterocyclyl, preferably a 3- to8-membered heterocyclyl. The terms “heterocyclyl” or “heterocyclo” as agroup or part of a group, refer to non-aromatic, fully saturated orpartially unsaturated cyclic groups (for example, 3 to 7 membermonocyclic, 7 to 11 member bicyclic, or containing a total of 3 to 10ring atoms) which have at least one heteroatom in at least one carbonatom-containing ring. Each ring of the heterocyclic group containing aheteroatom may have 1, 2, 3 or 4 heteroatoms selected N, O and/or S,where the N and S, where the N and S heteroatoms may be oxidized and theN heteroatoms may be quaternized. The heterocyclic group may be attachedat any heteroatom or carbon atom of the ring or ring system, wherevalence allows. The rings of multi-ring heterocycles may be fused,bridged and/or joined through one or more spiro atoms. A “substitutedheterocyclyl” refers to a heterocyclyl group having one or moresubstituent(s) (for example 1, 2 or 3 substituent(s), or 1 to 2substituent(s)), at any available point of attachment. Non limitingexemplary heterocyclic groups include oxiranyl, pyrrolidinyl,tetrahydrofuranyl, tetrahydrothiophenyl, dihydropyrrolyl,dihydrofuranyl, imidazolidinyl, pyrazolidinyl, imidazolinyl,pyrazolinyl, oxazolidinyl, isoxazolidinyl, oxazolinyl, isoxazolinyl,thiazolidinyl, isothiazolidinyl, thiazolinyl, piperidyl,tetrahydropyranyl, indolinyl, piperazinyl, 3-dioxolanyl, 1,4-dioxanyl,1,3-dioxolanyl, and 1,4-oxathianyl.

In particular embodiments, R¹ is heteroaryl. The term “heteroaryl”, asused herein, represents a stable 5- to 10-membered aromatic ring systemwhich consists of carbon atoms and from one to four heteroatoms selectedfrom the group consisting of N, O and S, and wherein the nitrogen andsulfur heteroatoms may optionally be oxidized, and the nitrogenheteroatom may optionally be quaternized. Preferably, said heteroaryl isa 5- to 6-membered aromatic ring. Examples of such heteroaryl groupsinclude, but are not limited to, furan, furazan, imidazole, isothiazole,isoxazole, oxadiazole, oxazole, pyrazine, pyrazole, pyridazine,pyridine, pyrimidine, pyrrole, tetrazole, thiadiazole, thiazole,thiophene, triazine, triazole, and N-oxides thereof. Preferably saidheteroaryl is furan.

The term “C₇₋₁₆aralkyl” or “C₇₋₁₆arylalkyl”, as a group or part of agroup, means an arylalkyl in which the aryl and alkyl are as previouslydescribed, wherein the aryl and alkyl together contain 7 to 16 carbonatoms. The bond to the parent moiety is through the alkyl. Examples ofC₇₋₁₆aralkyl radicals include benzyl, phenethyl, 3-(2-naphthyl)-butyl,and the like.

The term “C₇₋₁₆alkylaryl”, as a group or part of a group, means analkyl-aryl in which the aryl and alkyl are as previously described,wherein the aryl and alkyl together contain 7 to 16 carbon atoms. Thebond to the parent moiety is through the aryl. A non-limiting example ofa C₇₋₁₆alkylaryl is tolyl.

In particular embodiments, R¹ is heterocyclylC₁₋₆alkyl. The term“heterocyclylC₁₋₆alkyl”, as a group or part of a group, means aC₁₋₆alkyl as defined herein, wherein at least one hydrogen atom isreplaced by at least one heterocyclyl as defined herein, moreparticularly a 3- to 8-membered heterocyclyl, more particularly a 3- to6-membered heterocyclyl, and even more particularly a 3- to 5-memberedheterocyclyl.

In particular embodiments, R¹ is heteroarylC₁₋alkyl. The term“heteroarylC₁₋₆alkyl”, as a group or part of a group, means a C₁₋₆alkylas defined herein, wherein at least one hydrogen atom is replaced by atleast one heteroaryl as defined herein, more particularly a 5- to10-membered heteroaryl, more particularly a 5- to 6-membered heteroaryl.The bond to the parent moiety is through the alkyl.

In particular embodiments, R¹ is C₄₋₁₈cycloalkylalkyl, more particularlyC₄₋₈cycloalkylalkyl. The term “C₄₋₁₈cycloalkylalkyl” as a group or partof a group, means an cycloalkyl-alkyl in which the cycloalkyl and alkylare as previously described, wherein the cycloalkyl and alkyl togethercontain 4 to 10 carbon atoms. The bond to the parent moiety is throughthe alkyl. Examples of C₄₋₁₀cycloalkylalkyl radicals includecyclopropylmethyl, cyclopropylethyl, cyclopropylpropyl,cyclopentylmethyl, cyclopentylethyl, cyclopentylpropyl,cyclohexylmethyl, cyclohexylethyl, and cyclohexylpropyl.

In a particular embodiment, R¹ is C₄₋₁₀cycloalkenylalkyl. As usedherein, the term “C₄₋₁₀cycloalkenylalkyl” as a group or part of a group,means an cycloalkenyl-alkyl in which the cycloalkenyl and alkyl are asdefined herein, wherein the cycloalkenyl and alkyl together contain 4 to10 carbon atoms. The bond to the parent moiety is through the alkyl.

In particular embodiments, R¹⁰ is C₁₋₈alkylene. In further embodiments,R¹⁰ is C₁₋₆alkylene, more particularly C₁₋₄alkylene. Non-limitingexamples of C₁₋₆alkylene groups include methylene (—CH₂—), ethylene(—CH₂—CH₂—), methylmethylene (—CH(CH₃)—), 1-methyl-ethylene(—CH(CH₃)—CH₂—), n-propylene (—CH₂—CH₂—CH₂—), 2-methylpropylene(—CH₂—CH(CH₃)—CH₂—), 3-methylpropylene (—CH₂—CH₂—CH(CH₃)—), n-butylene(—CH₂—CH₂—CH₂—CH₂—), 2-methylbutylene (—CH₂—CH(CH₃)—CH₂—CH₂—),4-methylbutylene (—CH₂—CH₂—CH₂—CH(CH₃)—), pentylene and its chainisomers, and hexylene and its chain isomers.

In particular embodiments, R¹⁰ is an ether or oligoether of formula—R¹¹[OR¹²]_(m)R¹³—, wherein R¹¹, R¹² and R¹³ are independently from eachother C₁₋₄alkylene; and m is an integer from 1 to 4. In furtherembodiments, R¹¹, R¹² and R¹³ are independently from each otherC₁₋₃alkylene; and m is an integer from 1 to 3.

In particular embodiments, R¹⁰ is C₃₋₈cycloalkylene. As used herein, theterm “cycloalkylene”, by itself or as part of another substituent,refers to a cycloalkyl moiety as defined herein which is divalent.

In a particular embodiment, R¹⁰ is C₃₋₈cycloalkenylene. As used herein,the term “cycloalkenylene” by itself or as part of another substituent,refers to a cycloalkenyl as defined herein, which is divalent. Preferredcycloalkenylene rings contain 5 or 6 ring atoms, such ascyclopentenylene and cyclohexenylene.

In particular embodiments, R¹⁰ is C₆₋₁₀arylene. As used herein, the term“arylene”, by itself or as part of another substituent, refers to anaryl moiety as defined herein which is divalent.

In particular embodiments, R¹⁰ is C₂₋₁₂alkenylene, preferablyC₂₋₆alkenylene. The term “alkenylene” by itself or as part of anothersubstituent, refers to an alkenyl moiety as defined herein, which isdivalent.

In particular embodiments, R¹⁰ is C₂₋₁₂alkynylene, preferablyC₂₋₆alkynylene. The term “alkynylene” by itself or as part of anothersubstituent, refers to an alkynyl moiety as defined herein, which isdivalent.

In particular embodiments, R¹⁰ is heterocyclylene, preferably a 3- to8-membered heterocyclylene. The term “heterocyclylene” as a group orpart of a group, refers to a heterocyclyl moiety as defined herein,which is divalent.

In particular embodiments, R¹⁰ is heteroarylene. The term“heteroarylene”, as used herein, refers to a heteroaryl moiety asdefined herein, which is divalent.

In particular embodiments, R¹⁰ is C₇₋₁₆aralkylene. The term “aralkylene”as a group or part of a group, refers to an aralkyl moiety as definedherein, which is divalent.

In particular embodiments, R¹⁰ is “C₇₋₁₆alkylarylene”. The term“alkylarylene”, as a group or part of a group, refers to an alkylaryleneas defined herein, which is divalent.

In particular embodiments, R¹⁰ is heterocyclylC₁₋₆alkylene. The term“heterocyclylC₁₋₆alkylene”, as a group or part of a group, refers to aheterocyclylC₁₋₆alkyl moiety as defined herein, which is divalent.

In particular embodiments, R¹⁰ is heteroarylC₁₋₆alkylene. The term“heteroarylC₁₋₆alkylene”, as a group or part of a group, refers to aheteroarylC₁₋₆alkyl as defined herein, which is divalent.

In particular embodiments, R¹⁰ is C₄₋₁₀cycloalkylalkylene, moreparticularly C₄₋₈cycloalkylalkylene. The term “cycloalkylalkylene” as agroup or part of a group, refers to a cycloalkylalkylene as definedherein, which is divalent.

In a particular embodiment, R¹⁰ is C₄₋₁₀cycloalkenylalkylene. As usedherein, the term “C₄₋₁₀cycloalkenylalkylene” as a group or part of agroup, means an cycloalkenyl-alkylene in which the cycloalkenyl andalkylene are as defined herein, wherein the cycloalkenyl and alkylenetogether contain 4 to 10 carbon atoms.

The term “halo” or “halogen” as used herein refers to fluoro, chloro,bromo or iodo.

The term “amino” by itself or as part of another substituent, refers to—H₂.

The term “hydroxyl” by itself or as part of another substituent, refersto —OH.

The term “sulfhydryl”, by itself or as part of another substituent,refers to an —SH group.

The term “cyano”, by itself or as part of another substituent, refers toan —CN group.

The term “phosphonate” as used herein includes phosphonic acids, andesters or salts thereof. The term “phosphinate” as used herein includesphosphinic acids, and esters or salts thereof.

The metal or silicon oxides and hydroxides envisaged for use in themembranes described herein may be porous. The term “porous” as usedherein refers to solid materials with pores, i.e. cavities, channels orinterstices. The skilled person will understand that for the internalcoating of small pores, the groups R¹, R^(1′), and R¹⁰ as describedherein preferably are as small as possible. For example, R¹ and R^(1′)may be methyl or phenyl, and R¹⁰ methylene. Such short groups typicallyprovide the best protection against fouling. However, larger groups maystill be suitable for coating the outer surface of an oxide orhydroxide, or the inner surface of larger pores.

The present application relates to the field of membranes forfiltration, in particular ceramic microfiltration, ultrafiltration ornanofiltration membranes.

The term “nanofiltration”, “ultrafiltation” or “microfiltration” as usedherein refers to filtration using size exclusion by means of a porousmembrane, which will allow the passage of solvents while retarding thepassage of larger solute molecules, when a pressure gradient is appliedacross the membrane. Typically, microfiltration membranes have poresizes in the range of 0.1 micrometer, capable of retaining viruses andbacteria. Typically, ultrafiltration membranes have pore sizes in therange of 2 to 50 nm. Typically, nanofiltration membranes ischaracterized by molecular weight cut-off values between 200 and 1000Da, which makes 1-step removal of bacteria, viruses, natural organicmatter and micropollutants feasible, without complete removal ofinorganic salts. Therefore, the pore size (equivalent diameter) of thenanofiltration membrane is typically in the order of 1 nanometer.Typical values are between 0.5 (tight NF) and 5 nm (open NF).

Provided herein are methods of protecting such membranes againstfouling. The advantages of the membranes envisaged herein apply tomicrofiltration, ultrafiltration or nanofiltration membranes. Inparticular embodiments the membranes envisaged are nanofiltrationmembranes. Nanofiltration membranes have different applications. Oneimportant application is to partially soften potable water, allowingsome minerals to pass into the product water and thus increase thestability of the water and prevent it from being aggressive todistribution piping material. Additionally, nanofiltration membranes arefinding increasing use for purifying industrial effluents and minimizingwaste discharge.

The methods described herein comprise the grafting of a membranecomprising a silicon or metal oxide and/or hydroxide with an organicmoiety, by reacting said surface with an organometallic reagent, aphosphonate, a phosphinate, or an organosilane comprising said organicmoiety (or a protected form or precursor thereof). This will beexplained more in detail herein below.

Functionalized Inorganic Matrix

The methods described herein allow for the protection of a membranecomprising one or more oxides and/or hydroxides of metals or siliconagainst fouling. Additionally or alternatively, these methods may alsobe used for protecting metal or silicon oxides and/or metal hydroxideswhich will be incorporated in filtration membranes, against fouling.

In the present description, the one or more metal (or silicon) oxidesand/or metal (or silicon) hydroxides will be referred to as “inorganicmatrix”. The term “inorganic matrix” may refer to the metal (or silicon)oxides and/or metal (or silicon) hydroxides as such, or in the form of amembrane. Accordingly, the term “matrix” as used herein also refers to a“membrane”. In further particular embodiments the term “inorganicmatrix” also refers to an “inorganic membrane”, also denoted herein as a“ceramic membrane”.

In certain embodiments of the methods and applications envisaged herein,the functionalized matrix is an inorganic filtration membrane or ceramicfiltration membrane. As used herein, the expression “inorganicfiltration membrane” or “ceramic filtration membrane” is intended tocover inorganic membranes which can be used for microfiltration,ultrafiltration or nanofiltration. In particular embodiments, theinorganic filtration membranes are membranes which are suitable for thefiltration of aqueous compositions, more particularly compositionscomprising at least 50 wt % (weight percent) water, preferably at least70 wt % water, more preferably at least 90 wt % water. Such compositionsmay include, but are not limited to ground water, surface water, paperpulp effluents, emulsions such as oil/water wastes (as will be detailedbelow).

However, the membranes described herein may also show reduced foulingwhen used for the filtration of non-aqueous compositions. Accordingly,the functionalized membranes as described herein may also be used forthe treatment or filtration of non-aqueous compositions.

Ceramic filtration membranes may have a variety of shapes. In particularembodiments, the inorganic matrix described herein may be in the form ofa tube, sheet, disc or other shape that is permeable to substances insolution.

Techniques for preparing such membranes are well known in the art. Acommonly used technique for preparing such filtration membranes involvesdepositing one or more selective or filtering layers (comprising themetal/silicon hydroxides and/or oxides) of a few hundreds of nanometersor less in thickness onto a macroporous support matrix which providesthe mechanical strength. The filtering layer is usually obtained bydepositing mineral oxides onto the matrix, followed by a final heattreatment.

The skilled person will understand that an inorganic matrix for use in aliquid filtration membrane typically is porous. The pore size may dependon the type of filtration which is desired, such as microfiltration,ultrafiltration or nanofiltration (as explained above). In certainembodiments the inorganic matrix is porous, wherein the average poresize (or equivalent diameter) is between 0.5 to 200 nm, more preferablybetween 0.5 to 100 nm, more preferably between 0.5 to 50 nm, morepreferably between 0.5 to 30 nm, more preferably between 0.9 nm and 10.0nm, as measured by Molecular weight cut-off (indirect) and permporometryor nitrogen sorption techniques applied on powders of the top layer(direct), as known by the skilled person in the art.

In particular embodiments, the methods and applications envisaged hereinrelate to an organically functionalized inorganic matrix, wherein saidmatrix is a ceramic filtration membrane comprising a support made ofinorganic material coated with at least one separating membrane layerhaving an average pore size of is between 0.5 to 200 nm, more preferablybetween 0.5 to 100 nm, more preferably between 0.5 to 50 nm, morepreferably between 0.5 to 30 nm, more preferably between 0.9 to 10 nm.

Inorganic membranes envisaged for use in the context of the presentmethods comprise an inorganic matrix characterized by a structure whichcan be represented by M¹-OH and M¹-O-M¹ structure in which M¹ is a metalor silicon. In the envisaged methods, the surface modification typicallyinvolves the replacement of hydroxyl (—OH) groups provided on thesurface of the membrane by organic functional groups.

The one or more metal oxides and/or hydroxides of the inorganic matrixmay be crystalline or non-crystalline (amorphous), or may comprise amixture of crystalline and amorphous phases. If the inorganic matrixcomprises silicon oxide and/or silicon hydroxide, the silicon oxideand/or silicon hydroxide typically is amorphous. Thus, the inorganicmembranes envisaged herein typically comprise

-   -   an oxide and/or hydroxide of a metal; and/or    -   an amorphous silicon oxide.

The one or more elements M¹ in the hydroxides or oxides described hereinare preferably selected from titanium, zirconium, aluminium, silicon,strontium, yttrium, lanthanum, hafnium, thorium, iron, and manganese andvarious possible mixtures thereof. The above mentioned separatingmembrane layers are preferably formed from transition metal oxide(s),more specifically selected from group 4 of the IUPAC periodic table, inparticular Ti and/or Zr. In general, the inorganic matrix is preferablymade of titanium oxide and/or of zirconium oxide.

Examples of inorganic matrices that are envisaged for use in the methodsand applications described herein include for instance, but are notlimited to:

-   -   a zirconium oxide matrix having a pore size of 3 nm or a        titanium oxide matrix having a pore size of 0.9, 1 or 5 nm        (purchasable from Inopor);    -   a titanium oxide matrix with cut-off of 5 or 10 kDalton (pore        size on average 3 to 6 nm) (purchasable from Atech);    -   a mixed oxide matrix (titaniumoxide+zirconiumoxide) with cut-off        of 5 or 10 kDalton (pore size on average 3 to 6 nm) (purchasable        from Atech); and    -   a titaniumoxide matrix with cut-off of 1, 3, 5 or 8 kDalton        (pore size on average 1 to 5 nm) (purchasable from Tami        Industries).

The methods described herein aim to reduce the sensitivity of aninorganic matrix to fouling, by means of chemical surface modification,also denoted as “functionalization”. Thus, the methods described hereingenerate a functionalized matrix, more particularly an organicallyfunctionalized matrix. The terms “organically functionalized matrix” orsimply “functionalized matrix” as used herein refers to an inorganicmatrix of which the surface properties have been changed or modified(functionalized) by covalently binding an organic group R¹ or R¹⁰thereto.

In the context of the present application, the functionalization resultsin a functionalized matrix which is more hydrophobic (i.e. lesshydrophilic) compared to the matrix before functionalization(non-functionalized or native matrix). The increased hydrophobicity canbe assessed in various ways, e.g. via contact angle measurement or fluxmeasurements. More particularly, the functionalization as describedherein does not lead to an increased water flux, and will typicallyresult in a reduced water flux. In particular embodiments, the waterflux of the functionalized matrix is at least 10% below the water fluxof the non-functionalized matrix. Preferably, the water flux is measuredusing deionized water in a cross flow system, with a flow velocity of 2m/s, a trans membrane pressure (TMP) of 5 bar. In further embodiments,the water flux of the functionalized matrix is at least 20% below oreven at least 30% below the water flux of the non-functionalized matrix.

More particularly, the methods described herein involve functionalizingan inorganic matrix comprising an oxide and/or hydroxide of an elementM¹ which is a metal or silicon, by functionalization of the surface ofthe inorganic matrix with an organic moiety R¹ or R¹⁰ in order todecrease the sensitivity of the inorganic matrix to fouling. In certainembodiments, the inorganic matrix may be functionalized with two organicmoieties (e.g. R¹ and R^(1′)), for example via reaction of the inorganicmatrix with a reagent of formula R¹-M²-R^(1′) (see further), viareaction of the inorganic matrix with a mixture of reagents, and/or viaiteration of the method on the same inorganic matrix using differentreagents. R¹ and R^(1′) may be the same or different.

It has been found that the functionalization of the membranes withspecific organic moiety R¹ or R¹⁰ as described herein decreases thesensitivity of the inorganic matrix to fouling. In general, short R¹ orR¹⁰ moieties are preferred. Particularly preferred R¹ or R¹⁰ moietiesare provided herein below.

In particular embodiments, R¹ is selected from the list consisting ofC₁₋₈alkyl, C₆aryl, C₇₋₁₀alkylaryl, C₇₋₁₀arylalkyl, —R⁷[OR⁸]_(n)R⁹,C₃₋₆cycloalkyl, C₅₋₆cycloalkenyl, C₄₋₁₀cycloalkylalkyl,C₆₋₁₀cycloalkenylalkyl, C₂₋₈alkenyl, 3- to 6-membered heterocyclyl, 5-to 8-membered heteroaryl, heterocyclylC₁₋₄alkyl, heteroarylC₁₋₄alkyl andC₂₋₈alkynyl; wherein R⁷ and R⁸ are independently from each otherC₁₋₃alkylene; n is an integer from 1 to 3; and R⁹ is C₁₋₃ alkyl; and

R¹⁰ is selected from the list consisting of C₁₋₈alkylene, C₆arylene,C₇₋₁₀alkylarylene, C₇₋₁₀arylalkylene, —R¹¹[OR¹²]_(m)R¹³,C₃₋₆cycloalkylene, C₅₋₆cycloalkenylene, C₄₋₁₀cycloalkylalkylene,C₆₋₁₀cycloalkenylalkylene, C₂₋₈alkenylene, 3- to 6-memberedheterocyclylene, 5- to 8-membered heteroarylene,heterocyclylC₁₋₄alkylene, heteroarylC₁₋₄alkylene and C₂₋₈alkynylene;wherein R¹¹, R¹² and R¹³ are independently from each other C₁₋₃alkylene;and m is an integer from 1 to 3. In certain embodiments, R¹ is selectedfrom the list consisting of C₁₋₆alkyl, phenyl, C₇₋₈alkylaryl,C₇₋₈arylalkyl, —R⁷[OR⁸]_(n)R⁹, C₃₋₆cycloalkyl, C₅₋₆cycloalkyl,C₄₋₇cycloalkylalkyl, C₆₋₈cycloalkenylalkyl, C₂₋₆alkenyl, 3- to6-membered heterocyclyl, 5- to 6-membered heteroaryl,heterocyclylC₁₋₃alkyl, heteroarylC₁₋₃alkyl and C₂₋₆alkynyl; wherein R⁷and R⁸ are independently from each other C₁₋₂alkylene; n is an integerfrom 1 to 3; and R⁹ is C₁₋₂ alkyl; andR¹⁰ is selected from the list consisting of C₁₋₆alkylene, phenylene,C₇₋₈alkylarylene, C₇₋₈arylalkylene, —R¹¹[OR¹²]_(m)R¹³,C₃₋₆cycloalkylene, C₅₋₆cycloalkenylene, C₄₋₇cycloalkylalkylene,C₆₋₈cycloalkenylalkylene, C₂₋₆alkenylene, 3- to 6-memberedheterocyclylene, 5- to 6-membered heteroarylene,heterocyclylC₁₋₃alkylene, heteroarylC₁₋₃alkylene and C₂₋₆alkynylene;wherein R¹¹, R¹² and R¹³ are independently from each other C₁₋₂alkylene;and m is an integer from 1 to 3. In certain embodiments, R¹ is selectedfrom the list consisting of C₁₋₆alkyl, phenyl, benzyl, tolyl,—R⁷[OR⁸]_(n)R⁹, C₂₋₆alkenyl, furyl, 1-furylmethyl, and1,3-dioxolan-2-ylmethyl; and R¹⁰ is C₁₋₆alkylene; wherein R⁷ and R⁸ areindependently from each other C₁₋₂alkylene; n is an integer from 1 to 3;and R⁹ is C₁₋₂ alkyl.

In certain embodiments, R¹ is selected from the group consisting ofC₁₋₆alkyl, phenyl, and benzyl. Such groups were found to provideexcellent antifouling properties. In specific embodiments, R¹ isselected from the group consisting of C₁₋₆alkyl and phenyl, moreparticularly methyl or phenyl. In certain embodiments, R¹ is C₁₋₆alkyl,preferably selected from methyl, ethyl, and propyl.

Optionally, the membranes may further be grafted with one or moremoieties R^(1′) which can be the same or different from R¹. In certainembodiments, R¹ and R^(1′) are identical. If R¹ and R^(1′) are notidentical, R^(1′) typically is less bulky than R¹. More particularly,R^(1′) preferably comprises less carbon atoms than R¹.

In particular embodiments, said R¹, R^(1′), and/or R¹⁰ as describedabove may be further substituted with one or more groups selected fromhydroxyl, —OR⁴, amino, halo, sulfhydryl, —SR⁵, —COOH, and —COOR⁶;wherein R⁴, R⁵, and R⁶ are independently selected from C₁₋₆alkyl, haloand C₆₋₁₀aryl. In certain embodiments, the one or more substituents areindependently selected from hydroxyl, amino, halo, sulfhydryl, and—COOH.

The skilled person will understand that only a limited number ofhydrophilic substituents such as hydroxyl should be used in order toensure a functionalization which renders the inorganic matrix morehydrophobic compared to the native inorganic matrix. More particularly,the number and/or position of the optional substituents can be selectedso as to ensure a decreased hydrophilicity (i.e. an increasedhydrophobicity) of the grafted membrane compared to the native membrane(i.e. the membrane before grafting).

It is however envisaged that in other embodiments, said R¹, R^(1′)and/or R¹⁰ as described above may not be provided with furthersubstituents.

The functionalization or grafting of the surface of the inorganic matrixwith an organic moiety R¹ or R¹⁰ may be obtained by reacting theinorganic matrix with one or more organometallic reagents, phosphonates,phosphinates, and/or organosilanes. This will be explained in moredetail herein below.

Reaction with Organometallic Reagent

In particular embodiments, the method for protecting an oxide orhydroxide against fouling as described herein may involve grafting thesurface of the inorganic matrix with an organic moiety R¹ via reactionwith an organometallic reagent, such as a Grignard reagent and/or anorganolithium reagent.

A procedure for the functionalization of an inorganic matrix viareaction with organometallic chemistry suitable for use in the presentmethod, is based on the method for obtaining a functionalized matrix asdescribed in international patent application WO 2010/106167, which ishereby incorporated by reference. Thus, in certain embodiments, thereaction of the inorganic matrix with the organometallic reagentcomprises an appropriate pretreatment of the inorganic matrix, includingdrying the matrix; reacting the dried matrix in the presence of a drysolvent with said organometallic reagent, thereby obtaining afunctionalized matrix; and optionally, washing and drying thefunctionalized matrix.

The functionalization via reaction with an organometallic compound asdescribed in WO 2010/106167 results in the functionalization of thematrix with one or more R¹ (and optionally R^(1′)) moieties, as definedherein, that are directly bound covalently to an element M¹ (being ametal or silicon) on a surface of said matrix via a direct M¹-R¹ bond.More particularly, the direct M¹-R¹ bond can be obtained via a directM¹-C bond i.e. not including an oxygen bridge.

If M¹ is a metal, this can improve the stability of the obtained matrix,compared to grafting with an organosilane, which typically forms aM¹-O—Si—R covalent bond which is more sensitive to hydrolysis.

Organometallic reagents as used herein may be represented by formulaR¹-M², or formula R¹-M²-X, or formula R¹-M²-R^(1′), wherein R¹ andR^(1′) can be different or identical and are moieties as defined above,M² is a metal selected from group 1 or 2 of the IUPAC periodic table,more particularly selected from Li and/or Mg, and wherein X is halo. Itis noted that where R¹ and/or R^(1′) as defined above comprises afunctional group which is not compatible with organometallic compounds,such group should be provided in a protected form (i.e. with aprotective group). Protective groups are well known in the art and willnot be disclosed in detail herein.

In particular embodiments, the organometallic reagent is anorganolithium reagent or an organomagnesium reagent. An organolithiumreagent is an organometallic compound with a direct bond between acarbon and a lithium atom and may be represented by the general formulaR¹—Li wherein R¹ is a moiety as defined herein above. Preferredorganolithium compounds are C₁₋₄alkyllithium such as methyllithium, andphenyllithium. Reaction of an inorganic matrix with such organolithiumreagents can result in a functionalized matrix which is particularlyresistant to fouling.

An organomagnesium reagent is an organometallic compound with a directbond between a carbon and a magnesium atom and may be represented by thegeneral formula R¹—Mg—X (Grignard reagent) or R¹—Mg—R^(1′), wherein R¹and R^(1′) are moieties as defined herein and wherein R¹ and R^(1′) canbe different or identical, and wherein X is halo, and preferably bromo,chloro, or iodo. A preferred organometallic reagent for use in thepresent method is a Grignard reagent. Particularly preferred Grignardreagents are C₁₋₄alkyllmagnesium halide such as methylmagnesium halide,and phenylmagnesium halide. Reaction of an inorganic matrix with suchGrignard reagents can result in a functionalized matrix which isparticularly resistant to fouling.

In particular embodiments, of the matrix may be reacted with two or moredifferent organometallic reagents, thereby allowing to directly bind ona surface of an inorganic membrane two or more different types ofmoieties.

Reaction with Phosphonate or Phosphinate

In particular embodiments, the method for protecting an oxide orhydroxide against fouling as described herein may involve grafting thesurface of the inorganic matrix with an organic moiety R¹ or R¹⁰ viareaction with a phosphonate and/or a phosphinate. In contrast with thereaction with organometallic reagents as described above, somephosphonate reactions may be performed using aqueous solutions ororganic solutions which do not need to be dried. Nevertheless,phosphonate or phosphinate reactions may also be performed in driedorganic solvents.

Various procedures for the functionalization of an inorganic matrix viaa (condensation) reaction with phosphonates which are suitable for usein the present method are known in the art. An example of a suitableprocedure is the one described in patent application US 2002/0023573,which is hereby incorporated by reference.

The functionalization via reaction with an phosphonate or phosphinate asdescribed therein results in the functionalization of the matrix with aR¹ moiety, as defined herein, that are bound covalently to a metal (orsilicon) M¹ on a surface of said matrix via a covalent M¹-O—P—R¹ bond,more particularly via a covalent M¹-O—P—C bond. With phosphonates, thesame phosphorous atom may be bound to the matrix via a mono-, bi-, ortridentate bond (i.e. via one, two, or three P—O-M¹ bonds). TheM¹-O—P—R¹ bond typically provides sufficient stability for use of thefunctionalized material in filtration, for cleaning of the material,etc.

In particular embodiments, the inorganic matrix may be reacted with adiphosphonate or diphosphinate. This can result in the functionalizationof the matrix with a R¹⁰ moiety, as defined herein, that is bound to ametal (or silicon) M¹ on a surface of said matrix via two covalentbonds, forming a bridged structure, represented by M¹-O—P—R¹⁰—P—O-M¹.Accordingly, R¹⁰ can be bound to two elements M¹ (which can be the sameor different) of the inorganic matrix, thus forming a bridge. This canincrease the stability of the functionalized matrix. Again, withphosphonates, the same phosphorous atom may be bound to the matrix via amono-, bi-, or tridentate bond.

It is noted that where R¹ or R¹⁰ as defined above comprises a functionalgroup which is not compatible with the functionalization process (viareaction with organometallic reagents or phosphonates), such groupshould be provided in a protected form (i.e. with a protecting group),that is to be removed after functionalization. Protecting groups, andthe methods for removing them are well known in the art and will not bedisclosed in detail herein.

In particular embodiments, the grafting described herein may involvegrafting the surface of the inorganic matrix with an organic moiety R¹via reaction with a phosphonate reagent. More particularly, saidphosphonate reagent is a compound having a formula corresponding to thestructures herein below. In particular embodiments, said phosphonate isa compound of formula (I)

or a salt or ester thereof, wherein R¹ has the same meaning as describedabove.

Preferred salts or esters of the compound of formula (I) arephosphonates of formula (II)

wherein R¹ has the same meaning as described above; andwherein R² and R³ are independently selected from hydrogen, C₁₋₁₈alkyl,C₆₋₁₄aryl, and C₃₋₁₆cycloalkyl. In certain embodiments, R² and R³ areindependently selected from hydrogen, halo, and C₁₋₁₂alkyl. In esters orsalts of the compound of formula (II), at least one of R² and R³ is nothydrogen.

Preferred phosphinates are phosphinates of formula (III)

or a salt or ester thereof, wherein R¹ and R^(1′) are as defined above.

Preferred diphosphonates are compounds of formula (IV)

or a salt or ester thereof, wherein R¹⁰ has the same meaning asdescribed above.

In particular embodiments, the grafting described herein may involvegrafting the surface of the inorganic matrix with an organic moiety R¹or R¹⁰ via reaction with a phosphonate reagent, wherein said phosphonateis a compound selected from the group consisting of methylphosphonicacid, phenylphosphonic acid, 2-(2-ethoxyethoxy)ethylphosphonic acid,6-phosphonohexanoic acid,1-[2-(2-diethoxyphosphorylethoxy)ethoxy]-2-methoxy-ethane,5-diethoxyphosphorylhexan-1-ol, 10-diethoxyphosphoryldecanoic acid,methyl 10-diethoxyphosphoryldecanoate, and 3-phosphonopropylphosphonicacid. In certain embodiments, the phosphonate reagent ismethylphosphonic acid and/or phenylphosphonic acid.

In particular embodiments, the present method for protecting an oxide orhydroxide against fouling as may involve contacting the inorganic matrixwith a solution comprising the phosphonic acid, and letting thephosphonic acid react with the surface of the inorganic matrix.

The reaction may be carried out at room temperature, or at elevatedtemperatures, e.g. under reflux conditions. In preferred embodiments,the reaction is carried out at a temperature between 20° C. and 150° C.,and preferably between 20° C. and 100° C.

In order to obtain a sufficient functionalization of the inorganicmatrix, the reaction is preferably carried out during a period of atleast 30 minutes, preferably between one hour and 24 hours, underconditions of stirring and/or shaking of the reaction mixture, or whilefiltrating the reaction mixture through the membrane.

Optionally, the inorganic matrix may be washed after reaction, using anappropriate solvent, i.e. appropriate to dissolve the reaction products.Typically, this can be done using water, or the solvent applied in thesynthesis. The washing process can be repeated if necessary. Preferablywashing is done by means of filtration through the membrane pores, inparticular to prevent that reaction products would remain on the matrixand in the pores of the matrix. Preferably filtration is done underpressure.

The grafting procedure may further optionally comprise the step ofdrying the obtained matrix, preferably under vacuum. The drying of thematrix may be done in a similar way as described above for the reactionwith organometallic reagents.

Reaction with Organosilane Reagent

In particular embodiments, the method for protecting an oxide orhydroxide against fouling as described herein may involve grafting thesurface of the inorganic matrix with an organic moiety R¹ or R¹⁰ viareaction with an organosilane reagent.

Reaction of the inorganic matrix with an organosilane results in thefunctionalization of the matrix with a R¹ moiety which is boundcovalently to a metal (or silicon) M¹ on a surface of said matrix via acovalent M¹-O—Si—R¹ bond, more particularly via a covalent M¹-O—Si—Cbond.

As described above, the M¹-O—Si—R¹ bond typically is less stable than adirect M¹-R¹ bond if M¹ is metal. However, if M¹ is silicon, theM¹-O—Si—R¹ bond provides an excellent stability. In certain embodiments,R¹ is bound covalently to M¹ via a covalent M¹-O—Si—R¹ bond, providedthat M¹ is silicon.

In particular embodiments, the inorganic matrix may be reacted with adisilane. This can result in the functionalization of the matrix with aR¹⁰ moiety, as defined above, that is bound to M¹ via two covalentbonds, forming a bridged structure, represented by M¹-O—Si—R¹⁰—Si—O-M¹.Accordingly, R¹⁰ can be bound to two elements M¹ (which can be the sameor different) of the inorganic matrix, thus forming a bridge. This canincrease the stability of the functionalized matrix.

Various procedures for the functionalization of an inorganic matrix viaa (condensation) reaction with organosilanes which are suitable for usein the present method are known in the art. An example of a suitableprocedure is the one described in patent application US 2006/237361,which is hereby incorporated by reference.

In particular embodiments, the organosilane grafting described hereinmay involve grafting the surface of the inorganic matrix with an organicmoiety R¹ via reaction with an organosilane reagent of formula R¹XYZSi,wherein R¹, X, Y, and Z are directly bound to Si; and R¹ has the samemeaning as defined above. At least one of X, Y, and Z is a hydrolysablegroup, wherein the others are independently have the same meaning asR^(1′) as defined above. In particular embodiments, the organosilane isa compound of formula (R¹)₃XSi, wherein X is a hydrolysable group.Suitable hydrolysable groups include, but are not limited to halo, andC₁₋₈alkoxy such as methoxy (CH₃O—) or ethoxy (CH₃CH₂O—).

In particular embodiments, the organosilane grafting described hereinmay involve grafting the surface of the inorganic matrix with an organicmoiety R¹⁰ via reaction with a disilane reagent of formula(XYZ)SiR¹⁰Si(XYZ), wherein R¹⁰ has the same meaning as defined above.Again, at least one of X, Y and Z is a hydrolysable group, wherein theothers independently have the same meaning as R^(1′) as defined above.In particular embodiments, the disilane is a compound of formula(X′)₃Si—R¹⁰—Si(X′)₃.

In particular embodiments, the organosilane grafting may involve anappropriate pre-treatment of the inorganic surface, contacting theinorganic matrix with a solution comprising the organosilane reagent,and letting the organosilane reagent react with the surface of theinorganic matrix, as known in the art.

Repetition of the Functionalization

In particular embodiments of the method described herein, thefunctionalization via reaction with an organometallic reagent or aphosphonic acid reagent may be repeated one or more times on the sameinorganic matrix. Repeated modifications can for instance be applied toincrease the amount of organic functional group(s) on the surface of themembrane. However, as the functionalization described herein typicallyresults in a reduced flow it is preferred to provide the grafting as asubmonolayer, which means that the surface of the inorganic matrix isnot fully saturated with functional groups. In this way, the membranescan be protected against fouling while minimizing flux reduction.

Repeated functionalization may also permit to bind two or more differenttypes of organic groups directly on a surface of a filtration membrane.Alternatively or in combination therewith, different types of organicgroups can also be covalently bound by simultaneously reacting theinorganic matrix with two or more different organometallic reagents, ortwo or more different phosphonic acids as described above.

In particular embodiments, a functionalization using an organometallicreagent may be followed by a further functionalization using aphosphonic acid reagent, or vice versa.

Membrane

The methods envisaged herein result in functionalized inorganic matriceswhich can be used as filtration membranes and provide an increasedresistance to fouling compared to non-functionalized inorganic matrices.Moreover, the functionalization via a direct M¹-C bond, an M¹-O—P—Cbond, or an M¹-O—Si—C bond (particularly when M¹ is Si) provides asatisfactory chemical, mechanical, thermal and hydrothermal stability.

Accordingly, further provided herein are functionalized inorganicmatrices, obtainable by or obtained by the methods described herein.More particularly, such membrane may comprise an oxide and/or hydroxideof an element M¹ which is a metal or silicon, wherein the surface ofsaid inorganic matrix is grafted, preferably covalently grafted, with anorganic functional group R¹, via

-   -   a direct M¹-R¹ bond;    -   at least one M¹-O—P—R¹ bond;    -   a M¹-O—Si—R¹ bond;    -   a M¹-O—P—R¹⁰—P—O-M¹ bond; or    -   a M¹-O—Si—R¹⁰—Si—O-M¹ bond;        wherein R¹ and R¹⁰ are as defined above.

In particular embodiments, M¹ is selected from the group consisting oftitanium, zirconium, aluminium, silicon, strontium, yttrium, lanthanum,hafnium, thorium, iron, manganese, or combinations thereof. In certainembodiments, M¹ is Ti and/or Zr. In specific embodiments, the oxideand/or hydroxide of M¹ is titanium oxide or zirconium oxide.

In particular embodiments, the filtration membrane may comprise asupport made of inorganic material coated with at least one separatingmembrane layer made of the oxide and/or hydroxide of metal M¹ at thesurface. In certain embodiments, the oxide and/or hydroxide of M¹ may beprovided as particles in a mixed matrix membrane. For example, theparticles may be embedded in a polymer matrix. The preparation of mixedmatrix membranes is well-known in the art. For example, the particlesmay be assembled on the surface of a (porous) membrane, or the particlesmay be blended with a (polymeric) casting solution. An overview ofmanufacturing procedures is provided by Kim and Van der Bruggen(Environmental Pollution 2010, 158, 2335-2349). The particle size andamount of particles and (polymer) matrix material can be chosendepending on the required characteristics of the membranes. In certainembodiments, the membranes are porous, having an average pore size of0.5 nm to 200 nm, more particularly 0.5 nm to 30 nm, for example 0.9 nmto 10 nm.

As is known by a person skilled in the art, it is not easy to directlyanalyze the changes on the surface of a modified membrane toplayer,whether the modification is done by the procedures as described hereinor via other modification techniques known in the state of the art suchas silanation. This is due to the fact that the modification takes placein the pores of the thin toplayer, while the bulk of the membrane(support and intermediate layers) are not or hardly modified, such thatthe presence of the much thicker membrane support masks the propertiesof the membrane toplayer; and/or because of the curvature of themembrane, which may e.g. have a tubular shape. Therefore, an unsupportedmembrane toplayer material may be used in order to characterize theproperties of the supported membrane toplayer, which is made in exactlythe same way as the supported membrane toplayer. Suitablecharacterization methods for such samples include Thermal GravimetricAnalysis (TGA), IR spectroscopy solid state NMR, XPS and leaching testsor other methods known in the art, as described in international patentapplication WO 2010/106167, which is hereby incorporated by reference.

Flux measurements do not directly analyse the modification of themembrane surface, but are a suitable way to determine the effect of themembrane modification on the membrane performance. In case ofhydrophobic modification with e.g. alkyl chains, the flux of apolarsolvents will increase, while the flux of polar solvents such as waterwill be similar or decrease. Another indirect characterization techniquedetermining the effect of the membrane modification on the membraneperformance is a molecular weight cut-off (MWCO) measurement,permporometry and/or a (water) contact angle measurement. This isillustrated in the Examples (see further).

Use in Water Filtration

It has surprisingly been found that the organically functionalizedmatrices as envisaged herein are particularly suitable for use in watertreatment, more particularly water purification. Indeed, it has beenfound that despite the functionalization with organic moieties, which infact increases their hydrophobicity, the membranes remain suitable forfiltration of aqueous compositions. As used herein, the term “waterpurification” refers to purification of (or removal of contaminantsfrom) aqueous compositions comprising more than 50 wt % water, moreparticularly at least 70 wt % water.

More particularly it has been found that the membranes are resistant tofouling agents of aqueous compositions such as ground water or surfacewater. Most particularly the organically functionalized matrices are ofinterest in the treatment of ground water or surface water, as they havea reduced sensitivity for fouling by foulants such as humic acids incombination with inorganic salts (e.g. Ca⁺²), proteins, peptides, aminoacids, polysaccharides and transparent exopolymer particles (TEP). Butthe organically functionalized matrices are also of interest in thetreatment of different waste-waters as for example (but not limited to)paper and pulp effluents, and emulsions such as oil/water waste waters.

Inorganic matrices envisaged for use in water filtration are typicallymade of one or more metal oxides and/or metal hydroxides due to theirinherent hydrophilic nature. Typically, their surface chemistryessentially consists of a M¹-OH and M¹-O-M¹ structure in which M¹ is ametal or silicon. The methods and applications described herein envisagethe use of such inorganic matrices which have been organicallyfunctionalized.

Accordingly, envisaged herein is the use of organically functionalizedinorganic matrices comprising an oxide and/or hydroxide of a metal M¹for water treatment, whereby the matrices are characterized in thattheir surface is grafted, preferably covalently grafted, with an organicfunctional group. More particularly, the organic group is a group suchas but not limited to a group R¹ or R¹⁰ as defined above.

It is envisaged that the functionalization of the element M¹ in thematrix is not critical and can be ensured either through a direct bondwith the metal or through an oxygen bridge. In particular embodiments,the bond is a direct M¹-C bond, an M¹-O—P—C bond, or an M¹-O—Si—C bond.In particular embodiments M¹ is selected from the group consisting oftitanium, zirconium, aluminum, silicon, strontium, yttrium, lanthanum,hafnium, thorium, iron, manganese, or combinations thereof. Moreparticularly, the metal is titanium and/or zirconium.

The organically functionalized matrices for use as water treatmentmembranes can be obtained as described herein above.

Thus provided herein are methods of treating aqueous solutions, such asmethods for the removing impurities from aqueous solutions, comprisingfiltering said aqueous solutions with the matrices or membranesdescribed herein above obtainable by or obtained by the methodsdescribed herein above. In particular embodiments, the membranes areused for the (nano)filtration of aqueous compositions comprising atleast 50 wt % water, preferably at least 75 wt % water, and morepreferably at least 90 wt % water. In further particular embodiments,the water is groundwater, or surface water of industrial waste waters.

Practical examples where the anti-fouling effect is of criticalimportance include, but are not limited to, the production of drinkingwater from ground water or other sources of water, the purification ofdifferent waste waters including pulp and paper effluents, oil/watereffluents (from olive oil production, or oil/water emulsions found inwater that is used to pump up oil etc.)

-   -   Further provided herein is a method of purifying an aqueous        composition, said method comprising providing a filtration        membrane comprising a functionalized inorganic matrix comprising        an oxide and/or hydroxide of an element M¹ wherein M¹ is a metal        or silicon, characterized in that the surface of the inorganic        matrix is grafted with an organic functional group R¹ or R¹⁰ as        described herein; and    -   filtering said aqueous composition through said membrane so as        to obtain a purified aqueous composition.

Thus methods are provided herein for purifying an aqueous composition,the method comprising filtering said aqueous composition through afiltration membrane comprising a functionalized inorganic matrixcomprising an oxide and/or hydroxide of an element M¹ wherein M¹ is ametal or silicon, characterized in that the surface of the inorganicmatrix is grafted with an organic functional group R¹ or R¹⁰ asdescribed herein and obtaining in the filtrate a purified aqueouscomposition. In particular embodiments, the purification encompasses theremoval of contaminants such as oil, humics and/or other natural organicmatter, and/or polyelectrolytes. In particular embodiments, the methodsensure the removal of oils or petroleum products. In particularembodiments, at least 90% of the contaminants is removed from theaqueous composition via filtering through the membrane, preferably atleast 95%.

EXAMPLES

The following examples are provided for the purpose of illustrating theclaimed methods and applications and by no means are meant and in no wayshould be interpreted to limit the scope of the present invention.

1. Fouling Prevention in Surface and Ground Water Treatment

Commercially available titanium oxide (TiO₂) NF membranes were graftedwith various organic moieties applying both Phosphonic acids andGrignard grafting techniques. Hydrophilicity, pore size, and otherstructural changes after graftings were investigated by measuring watercontact angles, molecular weight cut-off values, and waterpermeabilities. Subsequently, the grafted membranes with the highestwater flux were subjected to fouling measurements with model foulantsmimicking the fouling in surface and ground water treatment for drinkingwater production, and with model fouling solutions mimicking the foulingin the effluents of pulp and paper industry. Similar tests wereperformed on a native (i.e. unmodified or non-functionalized) membraneas a control. This is explained further herein below.

1.A) Materials and Methods

Membranes and Chemicals

Asymmetric TiO₂ NF tubular membranes having an outer diameter of 1 cm,an inner diameter of 0.7 cm, and 12 cm in length (active membranesurface area ˜20 cm²) with an average pore diameter of 0.9 nm wereobtained from Inopor Gmbh, Germany.

All reagents and other chemicals were obtained from Sigma Aldrich:grafting reagents (methyl, phenyl, and hexadecyl phosphonic acids;methyl and phenyl magnesium bromide), model foulants (humic acid, meatpeptone, laminarin), toluene, CaCl₂, NaOH, and HCl (of pH adjustment).The alkaline cleaning agent P3 Ultrasil 110 was obtained from Ecolab.Reverse osmosis (RO) water with a conductivity of less than 15 μs/cm andpH 6.5 was used for all filtration experiments and for phosphonic acidsgrafting.

Grignard Grafting

TiO₂ membranes were grafted with methyl or phenyl groups using theorganometallic Grignard reagents methyl magnesium bromide and phenylmagnesium bromide, respectively. In a first step, the membranes wereproperly pretreated to remove the adsorbed water of the membranesurface. Subsequently, the pretreated membranes were contacted (withstirring and shaking or with filtration) for 48 hours to a reactionmixture of Grignard reagent in diethyl ether, under sufficiently dryatmosphere. The total metal oxide pore surface reacts with the Grignardreagent and the intended groups are grafted on the membrane. MgBr saltsare formed as side products of the reaction. These have been washed by aproper washing procedure. After washing, the membranes have been driedat 60° C. under vacuum before use in performance tests.

Phosphonic Acid Grafting

TiO₂ membranes were grafted with methyl, phenyl, and hexadecyl groupsusing methylphosphonic acid, phenylphosphonic acid, andhexadecylphosphonic acid, respectively.

In a first step, the membranes were immersed in a solution of methyl-,phenyl-, or hexadecylphosphonic acid (0.01 to 0.1 M) in water ortoluene, and treated for 4 hours at room temperature or for 4 hoursunder reflux at 90° C., under stirring and shaking. The modifiedmembranes were separated by pouring out the reaction solution after 4hours. Subsequently, the membranes were properly washed at roomtemperature with the reaction solvent (85-90 ml for 30 min with 5 timesrepetition), again under stirring and shaking. Thereafter, the membraneswere fixed in a dead-end set-up at a pressure of 2 bar for washing withwater inside of the pores. Subsequently, the membranes were dried atroom temperature before use in performance tests.

Water Contact Angle, Permeability, and MWCO Measurement

Grafted and ungrafted membranes were characterized by measuring theMolecular Weight Cut-Off (MWCO), the water contact angle, and the waterpermeability of the membranes.

For the MWCO measurement, the membranes were analyzed via Gel permeationchromatography using a Shimadzu system equipped with a pump (LC-20AT),Auto sampler (sil 20AC HT), column oven (CTO-20AC) and a refractiveindex detector (RID 10A)). The MWCO (i.e. the molecular weight of thesolute of which 90% is retained by the membrane) was determined usingthe method as described by I. Genné & G. Jonsson, C. Guizard,Harmonization of flux and MWCO characterization methodologies, posterpresentation in international Congress on membrane and MembraneProcesses (ICOM), 7-12 Jul. 2002, Toulouse, France. The water contactangle (CA) was calculated using a contact angle system OCA 15 plusmanufactured by Dataphysics with the software package SCA 20.

Pure water flux was measured in a cross flow system, with a flowvelocity of 2 m/s, a trans membrane pressure (TMP) of 5 bar.

Fouling Measurements

The following procedure was adopted to evaluate the fouling tendency ofall membranes:

-   1. A reverse osmosis (RO) water flux measurement is performed at    room temperature in cross-flow (2 m/s, 5 bar TMP), for 1 to 3 hours    in order to obtain a stable flux.-   2. Subsequently, fouling is induced by continuous filtration in    dead-end mode (to enhance the fouling effect) at room temperature    using a fouling solution, for 8 to 12 hours.-   3. After fouling, a RO water flux measurement was performed at room    temperature in cross-flow (again at 2 m/s and 5 bar TMP) to remove    the reversible part of the fouling. The measurements were performed    for 1 to 3 hours in order to obtain a stable flux.

The loss in water flux determined in this way, is a measure for theirreversible fouling. FIG. 2 graphically shows the RO water flux througha membrane before fouling, the foulant solution flux and the RO waterflux after fouling. The difference between the RO water flux afterfouling and the foulant solution flux is referred to as the amount ofreversible fouling while the difference between the RO water flux beforeand after fouling is referred to as the amount of irreversible fouling.Flux values were calculated based on the weight of the permeate, whichwas recorded automatically as function of time.

Chemical Cleaning

The organically fouled membranes were cleaned using the alkalinecleaning agent P3 ultrasil 110. The following solutions and filtrationconditions were used: 0.2 à 1% wt-solution of P₃ ultrasil 110 (i.e. pH 9to 12, conductivity 400 to 4220 μs/cm), temperature 46 to 60° C., crossflow with a flow velocity of about 4 m/s, TMP of 0.5 to 1 bar and afiltration time of 15 to 60 minutes. After cleaning, rinsing with ROwater was performed (using cross-flow filtration), and subsequently thewater permeability was determined.

1.B) Results

Membrane Functionalization

TiO₂ membranes were grafted with either methyl (M), phenyl (P), orhexadecyl (HD), via reaction with a phosphonic acid (PA) or a Grignardreagent (GR). The smaller methyl and phenyl groups were used to modifythe outer membrane surface as well as the inner pore surface of themembranes, whereas the hexadecyl functional groups were grafted to onlymodify the outer surface of the membranes. The resulting membranes aredenoted by a three or four letter code, wherein the last two lettersindicate the grafting method (PA or GR), and the first one or twoletters indicate the grafted group (M, P, or HD).

Membrane Characterization

In order to evaluate the impact of grafting of a specific functionalgroup applying a specific grafting method on the pore structure and thehydrophilicity of the membranes, the molecular weight cut-off (MWCO),water contact angle, and pure reverse osmosis (RO) water permeability ofthe native and all grafted membranes was measured. The experimentalresults are summarized in Table 1.

TABLE 1 MWCO, CA, and RO water permeability values of different modifiedmembranes in comparison to an unmodified native TiO₂ 0.9 nm NF membrane.MGR refers to methyl Grignard membranes, PGR to phenyl Grignardmembranes, MPA to methylphosphonic acid grafted membranes, PPA tophenylphosphonic acid grafted membranes and HDPA for hexadecylphosphonicacid grafted membranes. Membranes ID CA (°) Water permeability(l/hm²bar) MWCO (Da) Native 20 20 512 MPA 37 14 500 PGR 60 8 542 MGR 609 511 PPA 80 low — HDPA 124 zero —

The CA values show that the produced grafted membranes cover a widerange of hydrophilicity depending on the grafting technique and thegrafted functional group. The water contact angle values correlate withthe water permeabilities, indicating that an increased hydrophobicity ofthe membrane generally leads to a lower water permeability. The PPA andHDPA membranes are most hydrophobic (highest CA), leading to asignificantly reduced water permeability for the PPA membrane, and awater permeability of zero for the HDPA. For these membranes, the MWCOvalue was not measured, and no fouling experiments were performed.

For the other membranes, the MWCO values did not change significantlyafter the different modifications in comparison to unmodified membranes,indicating that no significant changes in pore size occurred.

Fouling Measurements

Fouling experiments were performed using model fouling solutionsmimicking the fouling in surface and ground water treatment, and modelfouling solutions mimicking the fouling in the treatment of effluents ofpulp and paper industry.

Ground and surface water typically contain a number of common foulants,more particularly humic acids with inorganic salts (e.g. Ca⁺²),proteins, peptides, amino acids, polysaccharides and transparentexopolymer particles (TEP). A number of synthetic compounds mimickingthese foulants are commercially available.

The fouling tendency of the grafted membranes in comparison to thenative membrane was determined by fouling measurements with thefollowing model foulants:

-   -   humic acid in combination with different concentrations of Ca²⁺        at different pH values, for mimicking natural organic material        (NOM) or humic materials;    -   laminarin gum for mimicking TEP foulants; and    -   meat peptone, as a model foulant for proteins.

A number of different aqueous solutions (foulant solutions) of thesemodel foulants and concentrations were prepared for measuring thefouling tendency of modified membranes in comparison with unmodifiedmembranes. Concentrations and pH values used mimic those of real groundand surface waters.

The same membranes were used for all three model foulants. In betweenthe measurements with the different type of foulants, the fouledmembranes were chemically cleaned (see further). The fouling of themembranes was assessed by determining the decline of the RO water fluxvalues for each membrane, normalized to the RO water flux beforefouling. The results of the fouling experiments are discussed hereinbelow.

Fouling Using Humic Acid:

for the fouling experiments using humic acid, commercially availablehumic acid (HA) was used as the model foulant, in a concentration of 10mg/L, in combination with 3 Ca²⁺ concentrations (1, 2 and 4 mmol) and 2pH levels (6, 5 and 9). It is known that inorganic ions, and inparticular Ca²⁺ can contribute to the adsorption of the organic matterto the membrane surface, and that a higher ionic strength of thesolution has a positive effect on the adhesion of humic acids. Thedifferent conditions were applied subsequently, without intermediatecleaning of the membranes.

The results of the experiments are shown in FIG. 1A, and show a clearwater flux decline and thus irreversible fouling of the native membraneunder all conditions. On the other hand, less fouling was observed withthe MPA and PGR membranes, whereas no fouling at all was observed withthe MGR membrane. The visual appearance of the membranes gave a similarindication of the degree of fouling Indeed, whereas the MGR membranestill had its original white color, the inside of the native membranehad a strong black color after the fouling measurements. Also the MPAand PGR membranes were colored due to fouling, but to a lesser extentthan the native membrane.

Fouling Using Laminarin:

It is well known that surface water is more fouling in the season ofalgae bloom. In these periods, large and sticky transparent exopolymerparticles (TEP) are formed predominantly by self-assembly of dissolvedprecursors, mostly dissolved polysaccharides released by microorganismsas algea, phytoplankton or bacterioplankton. Laminarin, a gum with amolecular size of ˜30 kD, is an important part of TEPs, and is thereforeused as a model foulant in this study. Laminarin concentrations in realwater streams typically are in the range of (0-0.5) mg/l.

The results of the fouling experiments using laminarin are shown in FIG.1B. Again, the native membrane is clearly fouled. The results of the PGRand the MGR membranes are similar to each other, and each show asignificantly lower fouling compared to the native membrane. Also thefouling of the MPA membrane is low compared to the native membrane.

Fouling Using Meat Peptone:

Next to humic acids, proteins, polysaccharides, fatty acids and aminoacids are the other main constituent of natural organic matter (NOM) inground and surface waters causing membrane fouling. Commercial meatpeptone, prepared by the enzymatic hydrolysis of selected animaltissues, contains these compounds and is therefore a suitable modelfoulant for these components. Again, concentrations were used whichmimics real streams: 5, 15 and 25 mg/L.

The results of the fouling experiments with meat peptone are shown inFIG. 1C, and confirm the positive effect of the grafting on the foulingbehavior. Indeed, the MGR and MPA membrane again show a remarkably lowfouling, whereas also the fouling of the PGR membrane is low compared tothe native membrane.

Fouling Using Wood Extracts

Pulp and paper mill process waters or effluents typically comprise acomplex mixture of wood compounds (lignin, hemicelluloses, and the like)and process chemicals (e.g. resin acids), which may have a polymeric,oligomeric, or monomeric nature.

A model solution to mimic the fouling tendency of pulp and paper millprocess waters was prepared, based on a wood extract solution extractedfrom wood at a high temperature provided by the Lappeenranta Universityof Technology in Finland. The wood extract solution was evaporated andthe resulting powder was used to make model solutions by diluting thepowder into water at a concentration of 1.1 and 2.2 g/L. The pH of themodel solutions was about 6.5. Such solutions comprise woodhemicelluloses and lignin at wide molar mass range and a minor amount ofwood lipophilic extractives, and have shown a high fouling tendency formany polymeric membranes.

Three grafted membranes (MGR, PGR and MPA) were used in foulingmeasurements using these model solutions. The results of the foulingexperiments are shown in table 2 and FIG. 1D and again show a positiveeffect of the grafting on the fouling behavior. More particularly, theMGR and PGR membrane show a remarkably low fouling, while the fouling ofthe MPA membrane is still significantly lower compared to the nativemembrane.

TABLE 2 before fouling Pulp&Paper 1.1 g/l Pulp&Paper 2.2 g/l MGR 1 1 0.9PGR 1 0.96 0.86 Native 1 0.36 0.18 MPA 1 0.71 0.55Membrane Cleaning

In between the measurements with the different foulants, all fouledmembranes were chemically cleaned with an alkaline cleaning agent. Aftercleaning, the RO water flux of the membranes was measured in order toevaluate the efficiency of the cleaning.

It was found that whereas all grafted membranes recovered completelyunder milder chemical cleaning conditions at a pH value of 10, thenative membrane could not cleaned at pH10. Instead, the native membranesrequired relative harsh chemical cleaning conditions at a pH value of12. The relative ease of cleaning of the grafted membranes indicatesthat the foulants have more or stronger interactions with the nativemembrane as compared to the grafted membranes, again showing thatgrafting of ceramic NF membranes diminishes their fouling behavior.

The results of the cleaning experiments also provide an indication ofthe excellent stability of the grafting and the strength offoulant-membrane interactions.

Conclusions

The above results clearly indicate that grafting of NF TiO₂ membranesvia reaction of the membrane with phosphonic acids or organometallicreagents can decrease their fouling tendency. In particular graftingwith methyl groups using the Grignard technique leads to membranes withan unparalleled low sensitivity to irreversible fouling.

Cleaning experiments showed that all graftings are stable in basic mediaup to pH 10 and allowed for a proper cleaning of the grafted membranes,thereby fully restoring their water flux and anti-fouling capacity. Allobtained fouling results show that grafting results in vast foulingresistance, making it very interesting to enhance the commercialapplication potential of ceramic NF membranes for water treatment.

2. Fouling Prevention in Oil/Water Separation

A huge amount of waste water streams exist which are contaminated withoil. Currently, oil production is one of the biggest sources ofoil-contaminated waste water.

Nevertheless, also several other industrial sectors produce sucheffluents.

Open ultrafiltration membranes (having pore sizes from 20 to 200 nm)offer a good separation option for the treatment of oil-contaminatedwater. Unfortunately, membrane fouling is a serious issue.

The present inventors have performed tests to evaluate the antifoulingproperties of the membranes described herein, when used for oilcontaminated water treatment. The tests were performed on a modeloil/water emulsion mimicking real oil-contaminated water resulting fromoil production and other oil-containing (waste) water streams.

For these tests three commercially available TiO₂ membranes (obtainablefrom Inopor, Germany) with a pore size of 30 nm were used. A first TiO₂membrane was grafted with methyl groups using Grignard grafting (seesection 1.A above) and a second TiO₂ membrane was grafted with methylgroups using phosphonic acid grafting (see section 1.A above). The thirdTiO₂ membrane was not grafted and was used as a control.

Fouling tests were performed with all three membranes to determine theirreversible fouling. The fouling tests were similar to the tests asdescribed above for Example 1 (here performed at 1 bar instead of at 5bar), but with the use of different oil/water model emulsions as foulantsolutions.

When comparing the membrane flow at the beginning and the end of thetests, the ungrafted TiO₂ membranes showed a flow reduction of more than50% due to irreversible fouling, whereas the flow reduction for thegrafted TiO₂ membranes was less than 10%. This indicates that thegrafted membranes are significantly less sensitive to irreversiblefouling.

This example clearly shows that the grafted membranes described hereinalso provide antifouling properties when using the membranes for thetreatment of oil contaminated water. The results further show that thepresent methods are not limited to porous membranes having a porediameter of about 1 nm as described in Example 1, but are also usefulfor much opener membranes.

What is claimed is:
 1. An antifouling treatment method of a hydrophilicmembrane comprising an oxide and/or hydroxide of silicon or a metal,comprising grafting a surface of the membrane comprising said oxideand/or hydroxide with an organic moiety R¹ or R¹⁰ by contacting saidsurface with an organometallic reagent, a phosphonate, a phosphinate, oran organosilane to obtain a treated membrane which is at least in parthydrophilic, wherein R¹ is selected from the group consisting ofC₁₋₁₂alkyl, C₆₋₁₀aryl, C₇₋₁₆alkylaryl, C₇₋₁₆arylalkyl, —R⁷[OR⁸]_(n)R⁹,C₃₋₈cycloalkyl, C₃₋₈cycloalkenyl, C₄₋₁₀cycloalkylalkyl,C₄₋₁₀cycloalkenylalkyl, C₂₋₁₂alkenyl, 3- to 8-membered heterocyclyl, 5-to 10-membered heteroaryl, heterocyclylC₁₋₆alkyl, heteroarylC₁₋₄alkyland C₂₋₁₂alkynyl; wherein R⁷ and R⁸ are independently from each otherC₁₋₄alkylene; n is an integer from 1 to 4; and R⁹ is C₁₋₄ alkyl; and R¹⁰is selected from the group consisting of C₁₋₈ alkylene, C₆₋₁₀arylene,C₇₋₁₆alkylarylene, C₇₋₁₆arylalkylene, —R¹¹[OR¹²]_(m)R¹³—,C₃₋₈cycloalkylene, C₃₋₈cycloalkenylene, C₄₋₁₀cycloalkylalkylene,C₄₋₁₀cycloalkenylalkylene, C₂₋₁₂alkenylene, 3- to 8-memberedheterocyclylene, 5- to 10-membered heteroarylene,heterocyclylC₁₋₆alkylene, heteroarylC₁₋₄alkylene and C₂₋₁₂alkynylene;wherein R¹¹, R¹², and R¹³ are independently from each otherC₁₋₄alkylene, and m is an integer from 1 to 4; wherein R¹ and R¹⁰ areoptionally substituted with one or more groups independently selectedfrom hydroxyl, —OR⁴, amino, halo, sulfhydryl, —SR⁵, —COOH, and —COOR⁶;wherein R⁴, R⁵, R⁶ are independently selected from C₁₋₆alkyl, halo andC₆₋₁₀aryl, and wherein the treated membrane has a ratio of waterpermeability compared to a same non-treated membrane of at least 8/20.2. The method according to claim 1, wherein said membrane comprises anoxide and/or hydroxide of an element M¹, and said surface of saidmembrane is grafted with an organic functional group R¹, via a directM¹-R¹ bond; at least one M¹-O—P—R¹ bond; a M¹-O—Si—R¹ bond; aM¹-O—P—R¹⁰—P—O-M¹ bond; or a M¹-O—Si—R¹⁰—Si—O-M¹ bond; wherein M¹ is ametal or silicon; and R¹ and R¹⁰ have the same meaning as defined inclaim
 1. 3. The method according to claim 1, wherein said organometallicreagent is a compound of the formula R¹-M², or of formula R¹-M²-X, or offormula R¹-M²-R^(1′); wherein M² is Li or Mg, and X is halo; R¹ has thesame meaning as in claim 1; and R^(1′) is, the same or different fromR¹, selected from the group consisting of C₁₋₁₂alkyl, C₆₋₁₀aryl,C₇₋₁₆alkylaryl, C₇₋₁₆arylalkyl, —R⁷[OR⁸]_(n)R⁹, C₃₋₈cycloalkyl,C₃₋₈cycloalkenyl, C₄₋₁₀cycloalkylalkyl, C₄₋₁₀cycloalkenylalkyl,C₂₋₁₂alkenyl, 3- to 8-membered heterocyclyl, 5- to 10-memberedheteroaryl, heterocyclylC₁₋₆alkyl, heteroarylC₁₋₄alkyl and C₂₋₁₂alkynyl;optionally substituted with one or more groups independently selectedfrom hydroxyl, —OR⁴, amino, halo, sulfhydryl, —SR⁵, —COOH, and —COOR⁶;wherein R⁴, R⁵, R⁶ are independently selected from C₁₋₆alkyl, halo andC₆₋₁₀aryl; R⁷ and R⁸ are independently from each other C₁₋₄alkylene; nis an integer from 1 to 4; and R⁹ is C₁₋₄ alkyl.
 4. The method accordingto claim 1, wherein said phosphonate or phosphinate is a compound chosenfrom formula (I)

or a salt or ester thereof, wherein R¹ has the same meaning as in claim1; or formula (III)

or a salt or ester thereof, wherein R¹ has the same meaning as in claim1; and R^(1′) is, the same or different from R¹, selected from the groupconsisting of C₁₋₁₂alkyl, C₆₋₁₀aryl, C₇₋₁₆alkylaryl, C₇₋₁₆arylalkyl,—R⁷[OR⁸]_(n)R⁹, C₃₋₈cycloalkyl, C₃₋₈cycloalkenyl, C₄₋₁₀cycloalkylalkyl,C₄₋₁₀cycloalkenylalkyl, C₂₋₁₂alkenyl, 3- to 8-membered heterocyclyl, 5-to 10-membered heteroaryl, heterocyclylC₁₋₆alkyl, heteroarylC₁₋₄alkyland C₂₋₁₂alkynyl; optionally substituted with one or more groupsindependently selected from hydroxyl, —OR⁴, amino, halo, sulfhydryl,—SR⁵, —COOH, and —COOR⁶; wherein R⁴, R⁵, R⁶ are independently selectedfrom C₁₋₆alkyl, halo and C₆₋₁₀aryl; R⁷ and R⁸ are independently fromeach other C₁₋₄alkylene; n is an integer from 1 to 4; and R⁹ is C₁₋₄alkyl; or formula (IV)

or a salt or ester thereof, wherein R¹⁰ has the same meaning as inclaim
 1. 5. The method according to claim 1, wherein R¹ is C₁₋₆alkyl,phenyl, or —R⁷[OR⁸]_(n)R⁹; wherein R⁷ and R⁸ are independently from eachother C₁₋₄alkylene; n is an integer from 1 to 4; and R⁹ is C₁₋₄ alkyl.6. The method according to claim 1, for protecting said membrane againstfouling when used for water treatment.
 7. The method according to claim1, wherein R¹ is C₁₋₆alkyl or phenyl; and R¹⁰ is C₁₋₆alkylene orphenylene.
 8. A method for the purification of an aqueous compositioncomprising the steps of (i) providing a functionalized at least in parthydrophilic inorganic matrix comprising an oxide and/or hydroxide of anelement M¹, wherein a surface of said inorganic matrix is grafted withan organic functional group R¹ or R¹⁰, wherein, M¹ is a metal orsilicon; R¹ is selected from the group consisting of C₁₋₁₂alkyl,C₆₋₁₀aryl, C₇₋₁₆alkylaryl, C₇₋₁₆arylalkyl, —R⁷[OR⁸]_(n)R⁹,C₃₋₈cycloalkyl, C₃₋₈cycloalkenyl, C₄₋₁₀cycloalkylalkyl,C₄₋₁₀cycloalkenylalkyl, C₂₋₁₂alkenyl, 3- to 8-membered heterocyclyl, 5-to 10-membered heteroaryl, heterocyclylC₁₋₆alkyl, heteroarylC₁₋₄alkyland C₂₋₁₂alkynyl; wherein R⁷ and R⁸ are independently from each otherC₁₋₄alkylene; n is an integer from 1 to 4; and R⁹ is C₁₋₄ alkyl; and R¹⁰is selected from the group consisting of C₁₋₈ alkylene, C₆₋₁₀arylene,C₇₋₆alkylarylene, C₇₋₁₆arylalkylene, —R¹¹[OR¹²]_(m)R¹³—,C₃₋₈cycloalkylene, C₃₋₈cycloalkenylene, C₄₋₁₀cycloalkylalkylene,C₄₋₁₀cycloalkenylalkylene, C₂₋₁₂alkenylene, 3- to 8-memberedheterocyclylene, 5- to 10-membered heteroarylene,heterocyclylC₁₋₆alkylene, heteroarylC₁₋₄alkylene and C₂₋₁₂alkynylene;wherein R¹¹, R¹², and R¹³ are independently from each otherC₁₋₄alkylene; wherein R¹ and R¹⁰ are optionally substituted with one ormore groups independently selected from hydroxyl, —OR⁴, amino, halo,sulfhydryl, —SR⁵, —COOH, and —COOR⁶; wherein R⁴, R⁵, R⁶ areindependently selected from C₁₋₆alkyl, halo and C₆₋₁₀aryl, and m is aninteger from 1 to 4; and wherein the treated membrane has a ratio ofwater permeability compared to a same non-treated membrane of at least8/20; and (ii) filtering said aqueous composition with saidfunctionalized inorganic matrix to obtain a purified aqueouscomposition.
 9. The method according to claim 8, wherein R¹ or R¹⁰ isgrafted on said surface via a direct M¹-R¹ bond; at least one M¹-O—P—R¹bond; a M¹-O—Si—R¹ bond; a M¹-O—P—R¹⁰—P—O-M¹ bond; or aM¹-O—Si—R¹⁰—Si—O-M¹ bond.
 10. The method according to claim 8, wherein,M¹ is selected from the group consisting of titanium, zirconium,aluminium, silicon, strontium, yttrium, lanthanum, hafnium, thorium,iron, manganese, or combinations thereof.
 11. The method according toclaim 8, wherein the oxide and/or hydroxide of M¹ is titanium oxide orzirconium oxide.
 12. The method according to claim 8, wherein R¹ isC₁₋₆alkyl, phenyl, or R⁷[OR⁸]_(n)R⁹; optionally substituted with one ormore groups independently selected from hydroxyl, —OR⁴, amino, halo,sulfhydryl, —SR⁵, —COOH, and —COOR⁶; wherein R⁴, R⁵, R⁶ areindependently selected from C₁₋₆alkyl, halo and C₆₋₁₀aryl; R⁷ and R⁸ areindependently from each other C₁₋₄alkylene; and n is an integer from 1to
 4. 13. The method according to claim 8, wherein said functionalizedinorganic matrix is a membrane comprising a support made of inorganicmaterial coated with at least one separating membrane layer made of theoxide and/or hydroxide of M¹ at the surface.
 14. The method according toclaim 8, for the purification of an aqueous composition comprising atleast 70 wt % water.
 15. The method according to claim 13, wherein themembrane is a porous membrane with an average pore size of 0.5 nm to 200nm.
 16. The method of claim 1, wherein the water permeability ismeasured using deionized water in a cross flow system, with a flowvelocity of 2 m/s, and a trans membrane pressure of 5 bar.
 17. Themethod of claim 8, wherein the water permeability is measured usingdeionized water in a cross flow system, with a flow velocity of 2 m/s,and a trans membrane pressure of 5 bar.